diff --git a/apps/Makefile b/apps/Makefile
index d6e8cffac..98141b448 100644
--- a/apps/Makefile
+++ b/apps/Makefile
@@ -86,4 +86,9 @@ $(app_objs): $(app_image_objs)
 
 epsilon.$(EXE): $(app_objs) $(app_image_objs)
 
+TO_REMOVE := apps/main.o apps/i18n.o
+TMP := $(app_objs) $(app_image_objs)
+VAR := $(filter-out $(TO_REMOVE), $(TMP))
+test.$(EXE): $(VAR)
+
 products += epsilon.$(EXE) $(app_objs) $(call INLINER_PRODUCTS,$(app_images))
diff --git a/apps/apps_container.cpp b/apps/apps_container.cpp
index b4c41e6b0..2b038e6e5 100644
--- a/apps/apps_container.cpp
+++ b/apps/apps_container.cpp
@@ -152,14 +152,25 @@ bool AppsContainer::dispatchEvent(Ion::Events::Event event) {
   if (event == Ion::Events::USBEnumeration) {
     if (Ion::USB::isPlugged()) {
       App::Snapshot * activeSnapshot = (activeApp() == nullptr ? appSnapshotAtIndex(0) : activeApp()->snapshot());
-      /* Just after a software update, the battery timer does not have time to
-       * fire before the calculator enters DFU mode. As the DFU mode blocks the
-       * event loop, we update the battery state "manually" here. */
-      updateBatteryState();
-      switchTo(usbConnectedAppSnapshot());
-      Ion::USB::DFU();
-      switchTo(activeSnapshot);
-      didProcessEvent = true;
+      if (activeApp() == nullptr || activeApp()->prepareForExit()) {
+        /* Just after a software update, the battery timer does not have time to
+         * fire before the calculator enters DFU mode. As the DFU mode blocks the
+         * event loop, we update the battery state "manually" here. */
+        updateBatteryState();
+        switchTo(usbConnectedAppSnapshot());
+        Ion::USB::DFU();
+        switchTo(activeSnapshot);
+        didProcessEvent = true;
+      } else {
+        /* activeApp()->prepareForExit() returned false, which means that the
+         * app needs another event loop to prepare for being switched off.
+         * Discard the current enumeration interruption.
+         * The USB host tries a few times in a row to enumerate the device, so
+         * hopefully the device will get another enumeration event soon and this
+         * time the device will be ready to go in DFU mode. Otherwise, the user
+         * needs to re-plug the device to go into DFU mode. */
+        Ion::USB::clearEnumerationInterrupt();
+      }
     } else {
       /* Sometimes, the device gets an ENUMDNE interrupts when being unplugged
        * from a non-USB communicating host (e.g. a USB charger). The interrupt
@@ -212,6 +223,7 @@ bool AppsContainer::processEvent(Ion::Events::Event event) {
 }
 
 void AppsContainer::switchTo(App::Snapshot * snapshot) {
+  assert(activeApp() == nullptr || activeApp()->prepareForExit());
   if (activeApp() && snapshot != activeApp()->snapshot()) {
     resetShiftAlphaStatus();
   }
diff --git a/apps/calculation/Makefile b/apps/calculation/Makefile
index c2b9bc190..7b797bea7 100644
--- a/apps/calculation/Makefile
+++ b/apps/calculation/Makefile
@@ -24,7 +24,5 @@ i18n_files += $(addprefix apps/calculation/,\
 tests += $(addprefix apps/calculation/test/,\
   calculation_store.cpp\
 )
-test_objs += $(addprefix apps/calculation/, calculation.o calculation_store.o)
 
 app_images += apps/calculation/calculation_icon.png
-
diff --git a/apps/code/app.cpp b/apps/code/app.cpp
index efc7e6a94..bedd3d0f1 100644
--- a/apps/code/app.cpp
+++ b/apps/code/app.cpp
@@ -46,23 +46,23 @@ bool App::Snapshot::lockOnConsole() const {
 
 void App::Snapshot::setOpt(const char * name, char * value) {
   if (strcmp(name, "script") == 0) {
-      m_scriptStore.deleteAllScripts();
-      char * separator = strchr(value, ':');
-      if (!separator) {
-        return;
-      }
-      *separator = 0;
-      const char * scriptName = value;
-      /* We include the 0 in the scriptContent to represent the importation
-       * status. It is set to 1 after addScriptFromTemplate. Indeed, this '/0'
-       * char has two goals: ending the scriptName and representing the
-       * importation status; we cannot set it to 1 before adding the script to
-       * storage. */
-      const char * scriptContent = separator;
-      Code::ScriptTemplate script(scriptName, scriptContent);
-      m_scriptStore.addScriptFromTemplate(&script);
-      m_scriptStore.scriptNamed(scriptName).toggleImportationStatus(); // set Importation Status to 1
+    m_scriptStore.deleteAllScripts();
+    char * separator = strchr(value, ':');
+    if (!separator) {
       return;
+    }
+    *separator = 0;
+    const char * scriptName = value;
+    /* We include the 0 in the scriptContent to represent the importation
+     * status. It is set to 1 after addScriptFromTemplate. Indeed, this '/0'
+     * char has two goals: ending the scriptName and representing the
+     * importation status; we cannot set it to 1 before adding the script to
+     * storage. */
+    const char * scriptContent = separator;
+    Code::ScriptTemplate script(scriptName, scriptContent);
+    m_scriptStore.addScriptFromTemplate(&script);
+    m_scriptStore.scriptNamed(scriptName).toggleImportationStatus(); // set Importation Status to 1
+    return;
   }
   if (strcmp(name, "lock-on-console") == 0) {
     m_lockOnConsole = true;
@@ -88,15 +88,15 @@ App::App(Container * container, Snapshot * snapshot) :
 }
 
 App::~App() {
+  assert(!m_consoleController.inputRunLoopActive());
   deinitPython();
 }
 
 bool App::handleEvent(Ion::Events::Event event) {
   if (event == Ion::Events::Home && m_consoleController.inputRunLoopActive()) {
-    // We need to return true here because we want to actually exit from the
-    // input run loop, which requires ending a dispatchEvent cycle.
-    m_consoleController.askInputRunLoopTermination();
-    m_consoleController.interrupt();
+    /* We need to return true here because we want to actually exit from the
+     * input run loop, which requires ending a dispatchEvent cycle. */
+    m_consoleController.terminateInputLoop();
     if (m_modalViewController.isDisplayingModal()) {
       m_modalViewController.dismissModalViewController();
     }
diff --git a/apps/code/app.h b/apps/code/app.h
index 58d007e3c..db1c0bfc6 100644
--- a/apps/code/app.h
+++ b/apps/code/app.h
@@ -37,6 +37,13 @@ public:
     ScriptStore m_scriptStore;
   };
   ~App();
+  bool prepareForExit() override {
+    if (m_consoleController.inputRunLoopActive()) {
+      m_consoleController.terminateInputLoop();
+      return false;
+    }
+    return true;
+  }
   StackViewController * stackViewController() { return &m_codeStackViewController; }
   ConsoleController * consoleController() { return &m_consoleController; }
 
diff --git a/apps/code/console_controller.cpp b/apps/code/console_controller.cpp
index 639d40ebe..13acc6965 100644
--- a/apps/code/console_controller.cpp
+++ b/apps/code/console_controller.cpp
@@ -33,7 +33,7 @@ ConsoleController::ConsoleController(Responder * parentResponder, App * pythonDe
   m_sandboxController(this, this),
   m_inputRunLoopActive(false)
 #if EPSILON_GETOPT
-      , m_locked(lockOnConsole)
+  , m_locked(lockOnConsole)
 #endif
 {
   m_selectableTableView.setMargins(0, Metric::CommonRightMargin, 0, Metric::TitleBarExternHorizontalMargin);
@@ -81,21 +81,30 @@ void ConsoleController::runAndPrintForCommand(const char * command) {
   m_consoleStore.deleteLastLineIfEmpty();
 }
 
+void ConsoleController::terminateInputLoop() {
+  assert(m_inputRunLoopActive);
+  m_inputRunLoopActive = false;
+  interrupt();
+}
+
 const char * ConsoleController::inputText(const char * prompt) {
   AppsContainer * a = (AppsContainer *)(app()->container());
   m_inputRunLoopActive = true;
 
+  // Set the prompt text
   m_selectableTableView.reloadData();
   m_selectableTableView.selectCellAtLocation(0, m_consoleStore.numberOfLines());
   m_editCell.setPrompt(prompt);
   m_editCell.setText("");
 
+  // Run new input loop
   a->redrawWindow();
   a->runWhile([](void * a){
       ConsoleController * c = static_cast<ConsoleController *>(a);
       return c->inputRunLoopActive();
   }, this);
 
+  // Reset the prompt line
   flushOutputAccumulationBufferToStore();
   m_consoleStore.deleteLastLineIfEmpty();
   m_editCell.setPrompt(sStandardPromptText);
@@ -145,9 +154,8 @@ bool ConsoleController::handleEvent(Ion::Events::Event event) {
   }
 #if EPSILON_GETOPT
   if (m_locked && (event == Ion::Events::Home || event == Ion::Events::Back)) {
-    if (inputRunLoopActive()) {
-      askInputRunLoopTermination();
-      interrupt();
+    if (m_inputRunLoopActive) {
+      terminateInputLoop();
     }
     return true;
   }
@@ -234,10 +242,10 @@ bool ConsoleController::textFieldShouldFinishEditing(TextField * textField, Ion:
 }
 
 bool ConsoleController::textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) {
-  if (event == Ion::Events::Up && inputRunLoopActive()) {
-    askInputRunLoopTermination();
-    // We need to return true here because we want to actually exit from the
-    // input run loop, which requires ending a dispatchEvent cycle.
+  if (event == Ion::Events::Up && m_inputRunLoopActive) {
+    m_inputRunLoopActive = false;
+    /* We need to return true here because we want to actually exit from the
+     * input run loop, which requires ending a dispatchEvent cycle. */
     return true;
   }
   if (event == Ion::Events::Up) {
@@ -251,8 +259,8 @@ bool ConsoleController::textFieldDidReceiveEvent(TextField * textField, Ion::Eve
 }
 
 bool ConsoleController::textFieldDidFinishEditing(TextField * textField, const char * text, Ion::Events::Event event) {
-  if (inputRunLoopActive()) {
-    askInputRunLoopTermination();
+  if (m_inputRunLoopActive) {
+    m_inputRunLoopActive = false;
     return false;
   }
   runAndPrintForCommand(text);
@@ -266,8 +274,8 @@ bool ConsoleController::textFieldDidFinishEditing(TextField * textField, const c
 }
 
 bool ConsoleController::textFieldDidAbortEditing(TextField * textField) {
-  if (inputRunLoopActive()) {
-    askInputRunLoopTermination();
+  if (m_inputRunLoopActive) {
+    m_inputRunLoopActive = false;
   } else {
 #if EPSILON_GETOPT
     /* In order to lock the console controller, we disable poping controllers
diff --git a/apps/code/console_controller.h b/apps/code/console_controller.h
index 3ee90997c..2a672ba33 100644
--- a/apps/code/console_controller.h
+++ b/apps/code/console_controller.h
@@ -31,8 +31,8 @@ public:
   void autoImport();
   void autoImportScript(Script script, bool force = false);
   void runAndPrintForCommand(const char * command);
-  bool inputRunLoopActive() { return m_inputRunLoopActive; }
-  void askInputRunLoopTermination() { m_inputRunLoopActive = false; }
+  bool inputRunLoopActive() const { return m_inputRunLoopActive; }
+  void terminateInputLoop();
 
   // ViewController
   View * view() override { return &m_selectableTableView; }
diff --git a/apps/probability/Makefile b/apps/probability/Makefile
index 510b0cf62..7b0765032 100644
--- a/apps/probability/Makefile
+++ b/apps/probability/Makefile
@@ -39,7 +39,6 @@ i18n_files += $(addprefix apps/probability/,\
 tests += $(addprefix apps/probability/test/,\
   erf_inv.cpp\
 )
-test_objs += $(addprefix apps/probability/law/, erf_inv.o)
 
 app_images += apps/probability/probability_icon.png
 
diff --git a/apps/regression/Makefile b/apps/regression/Makefile
index 57a950967..3065bc27f 100644
--- a/apps/regression/Makefile
+++ b/apps/regression/Makefile
@@ -45,33 +45,5 @@ i18n_files += $(addprefix apps/regression/,\
 tests += $(addprefix apps/regression/test/,\
   model.cpp\
 )
-test_objs += $(addprefix apps/regression/,\
-  regression_context.o\
-  store.o\
-)
-test_objs += $(addprefix apps/shared/,\
-  store_context.o\
-)
-test_objs += $(addprefix apps/shared/,\
-  curve_view_cursor.o\
-  curve_view_range.o\
-  double_pair_store.o\
-  interactive_curve_view_range.o\
-  interactive_curve_view_range_delegate.o\
-  memoized_curve_view_range.o\
-  store_context.o\
-)
-test_objs += $(addprefix apps/regression/model/,\
-  cubic_model.o\
-  exponential_model.o\
-  linear_model.o\
-  logarithmic_model.o\
-  logistic_model.o\
-  model.o\
-  power_model.o\
-  quadratic_model.o\
-  quartic_model.o\
-  trigonometric_model.o\
-)
 
 app_images += apps/regression/regression_icon.png
diff --git a/apps/regression/graph_controller.h b/apps/regression/graph_controller.h
index d5b45feef..b30ac092e 100644
--- a/apps/regression/graph_controller.h
+++ b/apps/regression/graph_controller.h
@@ -23,6 +23,11 @@ public:
   void viewWillAppear() override;
   void selectRegressionCurve();
   int selectedSeriesIndex() const { return *m_selectedSeriesIndex; }
+
+  // moveCursorHorizontally and Vertically are public to be used in tests
+  bool moveCursorHorizontally(int direction) override;
+  bool moveCursorVertically(int direction) override;
+
 private:
   constexpr static int k_maxLegendLength = 16;
   constexpr static int k_maxNumberOfCharacters = 50;
@@ -35,7 +40,6 @@ private:
 
   // SimpleInteractiveCurveViewController
   void reloadBannerView() override;
-  bool moveCursorHorizontally(int direction) override;
   Shared::InteractiveCurveViewRange * interactiveCurveViewRange() override;
   Shared::CurveView * curveView() override;
   bool handleEnter() override;
@@ -43,7 +47,6 @@ private:
   // InteractiveCurveViewController
   void initRangeParameters() override;
   void initCursorParameters() override;
-  bool moveCursorVertically(int direction) override;
   uint32_t modelVersion() override;
   uint32_t rangeVersion() override;
   bool isCursorVisible() override;
diff --git a/apps/regression/test/graph.cpp b/apps/regression/test/graph.cpp
new file mode 100644
index 000000000..1162e3451
--- /dev/null
+++ b/apps/regression/test/graph.cpp
@@ -0,0 +1,176 @@
+#include <quiz.h>
+#include <string.h>
+#include <assert.h>
+#include "../model/model.h"
+#include "../graph_controller.h"
+#include "../regression_context.h"
+#include "../store.h"
+
+using namespace Poincare;
+using namespace Regression;
+
+void load_in_store(
+    Regression::Store * store,
+    double * x0, double * y0, int numberOfPoints0,
+    double * x1 = nullptr, double * y1 = nullptr, int numberOfPoints1 = 0,
+    double * x2 = nullptr, double * y2 = nullptr, int numberOfPoints2 = 0)
+{
+  // Set the points and the regression type
+  if (numberOfPoints0 != 0 && x0 != nullptr && y0 != nullptr) {
+    for (int i = 0; i < numberOfPoints0; i++) {
+      store->set(x0[i], 0, 0, i);
+      store->set(y0[i], 0, 1, i);
+    }
+  }
+  if (numberOfPoints1 != 0 && x1 != nullptr && y1 != nullptr) {
+    for (int i = 0; i < numberOfPoints1; i++) {
+      store->set(x1[i], 1, 0, i);
+      store->set(y1[i], 1, 1, i);
+    }
+  }
+  if (numberOfPoints2 != 0 && x2 != nullptr && y2 != nullptr) {
+    for (int i = 0; i < numberOfPoints2; i++) {
+      store->set(x2[i], 2, 0, i);
+      store->set(y2[i], 2, 1, i);
+    }
+  }
+}
+
+class NavigationEvent {
+public:
+  enum class Direction {
+    Up,
+    Right,
+    Down,
+    Left
+  };
+  NavigationEvent(Direction d, int series, int dot) :
+    direction(d),
+    expectedSelectedSeries(series),
+    expectedSelectedDot(dot)
+  {}
+  Direction direction;
+  int expectedSelectedSeries;
+  int expectedSelectedDot;
+};
+
+void assert_navigation_is(
+    int numberOfEvents,
+    NavigationEvent * events,
+    int startingDotSelection,
+    int startingSeriesSelection,
+    double * x0, double * y0, int numberOfPoints0,
+    double * x1 = nullptr, double * y1 = nullptr, int numberOfPoints1 = 0,
+    double * x2 = nullptr, double * y2 = nullptr, int numberOfPoints2 = 0)
+{
+  assert(startingDotSelection >= 0);
+  Store store;
+  Shared::CurveViewCursor cursor;
+  uint32_t dummy;
+
+  int selectedDotIndex = startingDotSelection;
+  int selectedSeriesIndex = startingSeriesSelection;
+
+  load_in_store(&store, x0, y0, numberOfPoints0, x1, y1, numberOfPoints1, x2, y2, numberOfPoints2);
+
+  if (selectedDotIndex < store.numberOfPairsOfSeries(selectedSeriesIndex)) {
+    cursor.moveTo(
+        store.get(selectedSeriesIndex, 0, selectedDotIndex),
+        store.get(selectedSeriesIndex, 1, selectedDotIndex));
+  } else {
+    cursor.moveTo(
+        store.meanOfColumn(selectedSeriesIndex, 0),
+        store.meanOfColumn(selectedSeriesIndex, 1));
+  }
+
+  AppsContainerStorage container;
+  // We do not really care about the snapshot
+  App app(&container, container.appSnapshotAtIndex(0));
+
+  GraphController graphController(
+      &app, &app, nullptr,
+      &store,
+      &cursor,
+      &dummy, &dummy,
+      &selectedDotIndex,
+      &selectedSeriesIndex);
+
+
+  for (int i = 0; i < numberOfEvents; i++) {
+    NavigationEvent event = events[i];
+    if (event.direction == NavigationEvent::Direction::Up) {
+      graphController.moveCursorVertically(1);
+    } else if (event.direction == NavigationEvent::Direction::Right) {
+      graphController.moveCursorHorizontally(1);
+    } else if (event.direction == NavigationEvent::Direction::Down) {
+      graphController.moveCursorVertically(-1);
+    } else {
+      assert(event.direction == NavigationEvent::Direction::Left);
+      graphController.moveCursorHorizontally(-1);
+    }
+    quiz_assert(event.expectedSelectedDot == selectedDotIndex);
+    quiz_assert(event.expectedSelectedSeries == selectedSeriesIndex);
+  }
+}
+
+QUIZ_CASE(regression_navigation_1) {
+  constexpr int numberOfPoints0 = 4;
+  double x0[numberOfPoints0] = {2.0, 3.0, 2.0, 1.0};
+  double y0[numberOfPoints0] = {0.0, 1.0, 0.5, 5.0};
+
+  constexpr int numberOfPoints1 = 3;
+  double x1[numberOfPoints1] = {1.0, 10.0, 2.0};
+  double y1[numberOfPoints1] = {0.0, 25.0, 0.5};
+
+  constexpr int numberOfEvents = 7;
+  NavigationEvent events[numberOfEvents] = {
+    NavigationEvent(NavigationEvent::Direction::Down, 0, -1),
+    NavigationEvent(NavigationEvent::Direction::Down, 0, 2),
+    NavigationEvent(NavigationEvent::Direction::Down, 1, 2),
+    NavigationEvent(NavigationEvent::Direction::Down, 0, 0),
+    NavigationEvent(NavigationEvent::Direction::Down, 1, 0),
+    NavigationEvent(NavigationEvent::Direction::Down, 1, -1),
+    NavigationEvent(NavigationEvent::Direction::Down, 1, -1)
+  };
+  assert_navigation_is(numberOfEvents, events, numberOfPoints0, 0, x0, y0, numberOfPoints0, x1, y1, numberOfPoints1);
+}
+
+QUIZ_CASE(regression_navigation_2) {
+  constexpr int numberOfPoints0 = 4;
+  double x0[numberOfPoints0] = {8.0, 9.0, 10.0, 10.0};
+  double y0[numberOfPoints0] = {2.0, 5.0, 1.0, 2.0};
+
+  constexpr int numberOfPoints1 = 3;
+  double x1[numberOfPoints1] = {10.0, 12.0, 5.0};
+  double y1[numberOfPoints1] = {2.0, 0.0, 8.0};
+
+  constexpr int numberOfEvents = 6;
+  NavigationEvent events[numberOfEvents] = {
+    /* FIXME
+     * Because of double computation error, the regression curve of the series 0
+     * is above its mean point.
+    NavigationEvent(NavigationEvent::Direction::Down, 1, -1),
+     * */
+    NavigationEvent(NavigationEvent::Direction::Down, 0, -1),
+    NavigationEvent(NavigationEvent::Direction::Down, 0, numberOfPoints0),
+    NavigationEvent(NavigationEvent::Direction::Down, 0, -1),
+    NavigationEvent(NavigationEvent::Direction::Down, 0, 3),
+    NavigationEvent(NavigationEvent::Direction::Down, 1, 0),
+    NavigationEvent(NavigationEvent::Direction::Down, 0, 2)
+  };
+  assert_navigation_is(numberOfEvents, events, numberOfPoints1, 1, x0, y0, numberOfPoints0, x1, y1, numberOfPoints1);
+}
+
+QUIZ_CASE(regression_navigation_3) {
+  constexpr int numberOfPoints = 4;
+  double x[numberOfPoints] = {1.0, 2.0, 3.0, 4.0};
+  double y[numberOfPoints] = {2.0, 2.0, 2.0, 2.0};
+
+  constexpr int numberOfEvents = 3;
+  NavigationEvent events[numberOfEvents] = {
+    NavigationEvent(NavigationEvent::Direction::Down, 0, -1),
+    NavigationEvent(NavigationEvent::Direction::Down, 1, -1),
+    NavigationEvent(NavigationEvent::Direction::Down, 2, -1),
+  };
+  assert_navigation_is(numberOfEvents, events, 2, 0, x, y, numberOfPoints, x, y, numberOfPoints, x, y, numberOfPoints);
+}
diff --git a/apps/sequence/Makefile b/apps/sequence/Makefile
index 2941b50fb..76354d74c 100644
--- a/apps/sequence/Makefile
+++ b/apps/sequence/Makefile
@@ -34,7 +34,5 @@ i18n_files += $(addprefix apps/sequence/,\
 tests += $(addprefix apps/sequence/test/,\
   sequence.cpp\
 )
-test_objs += $(addprefix apps/sequence/, sequence.o sequence_store.o sequence_context.o cache_context.o)
-test_objs += $(addprefix apps/shared/, expression_model.o  expression_model_store.o function.o function_store.o)
 
 app_images += apps/sequence/sequence_icon.png
diff --git a/apps/sequence/sequence.cpp b/apps/sequence/sequence.cpp
index 5cf80f9ff..d7bedbfef 100644
--- a/apps/sequence/sequence.cpp
+++ b/apps/sequence/sequence.cpp
@@ -96,14 +96,14 @@ void Sequence::setInitialRank(int rank) {
 
 Poincare::Expression Sequence::firstInitialConditionExpression(Context * context) const {
   if (m_firstInitialConditionExpression.isUninitialized()) {
-    m_firstInitialConditionExpression = PoincareHelpers::ParseAndReduce(m_firstInitialConditionText, *context);
+    m_firstInitialConditionExpression = PoincareHelpers::ParseAndSimplify(m_firstInitialConditionText, *context);
   }
   return m_firstInitialConditionExpression;
 }
 
 Poincare::Expression Sequence::secondInitialConditionExpression(Context * context) const {
   if (m_secondInitialConditionExpression.isUninitialized()) {
-    m_secondInitialConditionExpression = PoincareHelpers::ParseAndReduce(m_secondInitialConditionText, *context);
+    m_secondInitialConditionExpression = PoincareHelpers::ParseAndSimplify(m_secondInitialConditionText, *context);
   }
   return m_secondInitialConditionExpression;
 }
diff --git a/apps/shared/Makefile b/apps/shared/Makefile
index 35ed31960..db1d6dd7f 100644
--- a/apps/shared/Makefile
+++ b/apps/shared/Makefile
@@ -86,5 +86,3 @@ app_objs += $(addprefix apps/shared/,\
   vertical_cursor_view.o\
   zoom_parameter_controller.o\
 )
-
-test_objs += $(addprefix apps/shared/, storage_expression_model.o storage_function.o storage_cartesian_function.o)
diff --git a/apps/shared/expression_model.cpp b/apps/shared/expression_model.cpp
index 4dfecbbe8..bc7362e85 100644
--- a/apps/shared/expression_model.cpp
+++ b/apps/shared/expression_model.cpp
@@ -21,7 +21,7 @@ const char * ExpressionModel::text() const {
 
 Poincare::Expression ExpressionModel::expression(Poincare::Context * context) const {
   if (m_expression.isUninitialized()) {
-    m_expression = PoincareHelpers::ParseAndReduce(m_text, *context);
+    m_expression = PoincareHelpers::ParseAndSimplify(m_text, *context);
   }
   return m_expression;
 }
diff --git a/apps/shared/poincare_helpers.h b/apps/shared/poincare_helpers.h
index 90c0745cd..a9a2b9ef6 100644
--- a/apps/shared/poincare_helpers.h
+++ b/apps/shared/poincare_helpers.h
@@ -37,10 +37,6 @@ inline T ApproximateToScalar(const char * text, Poincare::Context & context) {
   return Poincare::Expression::approximateToScalar<T>(text, context, Poincare::Preferences::sharedPreferences()->angleUnit());
 }
 
-inline Poincare::Expression ParseAndReduce(const char * text, Poincare::Context & context) {
-  return Poincare::Expression::ParseAndReduce(text, context, Poincare::Preferences::sharedPreferences()->angleUnit());
-}
-
 inline Poincare::Expression ParseAndSimplify(const char * text, Poincare::Context & context) {
   return Poincare::Expression::ParseAndSimplify(text, context, Poincare::Preferences::sharedPreferences()->angleUnit());
 }
diff --git a/apps/shared/storage_expression_model.cpp b/apps/shared/storage_expression_model.cpp
index 66a143b2b..234875015 100644
--- a/apps/shared/storage_expression_model.cpp
+++ b/apps/shared/storage_expression_model.cpp
@@ -39,7 +39,12 @@ Expression StorageExpressionModel::expressionReduced(Poincare::Context * context
   if (m_expression.isUninitialized()) {
     assert(!isNull());
     Ion::Storage::Record::Data recordData = value();
-    m_expression = Expression::ExpressionFromAddress(expressionAddressForValue(recordData), expressionSizeForValue(recordData)).reduce(*context, Preferences::sharedPreferences()->angleUnit());
+    m_expression = Expression::ExpressionFromAddress(expressionAddressForValue(recordData), expressionSizeForValue(recordData));
+    PoincareHelpers::Simplify(&m_expression, *context);
+    // simplify might return an uninitialized Expression if interrupted
+    if (m_expression.isUninitialized()) {
+      m_expression = Expression::ExpressionFromAddress(expressionAddressForValue(recordData), expressionSizeForValue(recordData));
+    }
   }
   return m_expression;
 }
@@ -82,8 +87,7 @@ Ion::Storage::Record::ErrorStatus StorageExpressionModel::setContent(const char
     // Compute the expression to store, without replacing symbols
     expressionToStore = Expression::Parse(c);
     if (!expressionToStore.isUninitialized()) {
-      Symbol xUnknown = Symbol(Symbol::SpecialSymbols::UnknownX);
-      expressionToStore = expressionToStore.replaceSymbolWithExpression(Symbol("x", 1), xUnknown);
+      expressionToStore = expressionToStore.replaceUnknown(Symbol('x')); //TODO Beware of non x unknowns! (for instance whe sequences are in the storage)
     }
   }
   return setExpressionContent(expressionToStore);
diff --git a/apps/shared/storage_expression_model_list_controller.cpp b/apps/shared/storage_expression_model_list_controller.cpp
index dda78d027..d11522dd1 100644
--- a/apps/shared/storage_expression_model_list_controller.cpp
+++ b/apps/shared/storage_expression_model_list_controller.cpp
@@ -8,10 +8,9 @@ namespace Shared {
 
 StorageExpressionModelListController::StorageExpressionModelListController(Responder * parentResponder, I18n::Message text) :
   ViewController(parentResponder),
-  m_addNewModel(),
-  m_memoizedCellHeight {-1, -1, -1, -1, -1},
-  m_cumulatedHeightForSelectedIndex(-1)
+  m_addNewModel()
 {
+  resetMemoization();
   m_addNewModel.setMessage(text);
 }
 
@@ -20,7 +19,7 @@ void StorageExpressionModelListController::tableSelectionDidChange(int previousS
   int currentSelectedRow = selectedRow();
 
   // The previously selected cell's height might have changed.
-  m_memoizedCellHeight[currentSelectedMemoizedIndex] = -1;
+  m_memoizedCellHeight[currentSelectedMemoizedIndex] = k_resetedMemoizedValue;
 
   // Update m_cumulatedHeightForSelectedIndex if we scrolled one cell up/down
   if (currentSelectedRow == previousSelectedRow + 1) {
@@ -29,7 +28,7 @@ void StorageExpressionModelListController::tableSelectionDidChange(int previousS
     for (int i = 0; i < k_memoizedCellHeightsCount - 1; i++) {
       m_memoizedCellHeight[i] = m_memoizedCellHeight[i+1];
     }
-    m_memoizedCellHeight[k_memoizedCellHeightsCount-1] = -1;
+    m_memoizedCellHeight[k_memoizedCellHeightsCount-1] = k_resetedMemoizedValue;
     // Update m_cumulatedHeightForSelectedIndex
     if (previousSelectedRow >= 0) {
       m_cumulatedHeightForSelectedIndex+= memoizedRowHeight(previousSelectedRow);
@@ -43,7 +42,7 @@ void StorageExpressionModelListController::tableSelectionDidChange(int previousS
     for (int i = k_memoizedCellHeightsCount - 1; i > 0; i--) {
       m_memoizedCellHeight[i] = m_memoizedCellHeight[i-1];
     }
-    m_memoizedCellHeight[0] = -1;
+    m_memoizedCellHeight[0] = k_resetedMemoizedValue;
     // Update m_cumulatedHeightForSelectedIndex
     if (currentSelectedRow >= 0) {
       m_cumulatedHeightForSelectedIndex-= memoizedRowHeight(currentSelectedRow);
@@ -63,7 +62,7 @@ KDCoordinate StorageExpressionModelListController::memoizedRowHeight(int j) {
   constexpr int halfMemoizationCount = k_memoizedCellHeightsCount/2;
   if (j >= currentSelectedRow - halfMemoizationCount && j <= currentSelectedRow + halfMemoizationCount) {
     int memoizedIndex = j - (currentSelectedRow - halfMemoizationCount);
-    if (m_memoizedCellHeight[memoizedIndex] < 0) {
+    if (m_memoizedCellHeight[memoizedIndex] == k_resetedMemoizedValue) {
       m_memoizedCellHeight[memoizedIndex] = expressionRowHeight(j);
     }
     return m_memoizedCellHeight[memoizedIndex];
@@ -83,7 +82,7 @@ KDCoordinate StorageExpressionModelListController::memoizedCumulatedHeightFromIn
     return notMemoizedCumulatedHeightFromIndex(j);
   }
   // Recompute the memoized cumulatedHeight if needed
-  if (m_cumulatedHeightForSelectedIndex < 0) {
+  if (m_cumulatedHeightForSelectedIndex == k_resetedMemoizedValue) {
     m_cumulatedHeightForSelectedIndex = notMemoizedCumulatedHeightFromIndex(currentSelectedRow);
   }
   /* Compute the wanted cumulated height by adding/removing memoized cell
@@ -226,9 +225,9 @@ bool StorageExpressionModelListController::isAddEmptyRow(int j) {
 }
 
 void StorageExpressionModelListController::resetMemoization() {
-  m_cumulatedHeightForSelectedIndex = -1;
+  m_cumulatedHeightForSelectedIndex = k_resetedMemoizedValue;
   for (int i = 0; i < k_memoizedCellHeightsCount; i++) {
-    m_memoizedCellHeight[i] = -1;
+    m_memoizedCellHeight[i] = k_resetedMemoizedValue;
   }
 }
 
diff --git a/apps/shared/storage_expression_model_list_controller.h b/apps/shared/storage_expression_model_list_controller.h
index 7b2353eae..1d5b2961b 100644
--- a/apps/shared/storage_expression_model_list_controller.h
+++ b/apps/shared/storage_expression_model_list_controller.h
@@ -35,11 +35,28 @@ protected:
   virtual StorageExpressionModelStore * modelStore() = 0;
   virtual InputViewController * inputController() = 0;
   EvenOddMessageTextCell m_addNewModel;
+protected:
+  // Memoization
+  static constexpr int k_memoizedCellHeightsCount = 7;
+  /* We use memoization to speed up indexFromHeight(offset) in the children
+   * classes: if offset is "around" the memoized cumulatedHeightForIndex, we can
+   * compute its value easily by adding/substracting memoized row heights. We
+   * thus need to memoize 3 cells (see under for explanation on the 3) above the
+   * selected one, and 3 under, which gives 7 cells.
+   * 3 is the maximal number of non selected visible rows if the selected cell
+   * is completely [on top/at the bottom] of the screen. To compute this value:
+   * (ScreenHeight - Metric::TitleBarHeight - Metric::TabHeight - ButtonRowHeight
+   * - currentSelectedRowHeight) / Metric::StoreRowHeight
+   *   =  (240-18-27-20-50)/50 = 2.5 */
+  static_assert(StorageExpressionModelListController::k_memoizedCellHeightsCount % 2 == 1, "StorageExpressionModelListController::k_memoizedCellHeightsCount should be odd.");
+  /* We memoize values for indexes around the selectedRow index.
+   * k_memoizedCellHeightsCount needs to be odd to compute things such as:
+   * constexpr int halfMemoizationCount = k_memoizedCellHeightsCount/2;
+   * if (j < selectedRow - halfMemoizationCount
+   *   || j > selectedRow + halfMemoizationCount) { ... } */
 private:
   // Memoization
-  static constexpr int k_memoizedCellHeightsCount = 5;
-  static_assert(StorageExpressionModelListController::k_memoizedCellHeightsCount == 5, "Wrong array size in initialization of StorageExpressionModelListController::m_memoizedCellHeight.");
-static_assert(StorageExpressionModelListController::k_memoizedCellHeightsCount % 2 == 1, "StorageExpressionModelListController::k_memoizedCellHeightsCount should be odd to be able to compute the middle element.");
+  static constexpr int k_resetedMemoizedValue = -1;
   void resetMemoization();
   virtual KDCoordinate notMemoizedCumulatedHeightFromIndex(int j) = 0;
   KDCoordinate m_memoizedCellHeight[k_memoizedCellHeightsCount];
diff --git a/apps/shared/storage_function_list_controller.cpp b/apps/shared/storage_function_list_controller.cpp
index a555a4c76..d15d10f8f 100644
--- a/apps/shared/storage_function_list_controller.cpp
+++ b/apps/shared/storage_function_list_controller.cpp
@@ -4,6 +4,7 @@
 namespace Shared {
 
 static inline int max(int x, int y) { return x > y ? x : y; }
+static inline int min(int x, int y) { return x < y ? x : y; }
 
 StorageFunctionListController::StorageFunctionListController(Responder * parentResponder, ButtonRowController * header, ButtonRowController * footer, I18n::Message text) :
   StorageExpressionModelListController(parentResponder, text),
@@ -81,6 +82,42 @@ int StorageFunctionListController::indexFromCumulatedWidth(KDCoordinate offsetX)
   }
 }
 
+int StorageFunctionListController::indexFromCumulatedHeight(KDCoordinate offsetY) {
+  if (offsetY == 0) {
+    return 0;
+  }
+
+  /* We use memoization to speed up this method: if offsetY is "around" the
+   * memoized cumulatedHeightForIndex, we can compute its value easily by
+   * adding/substracting memoized row heights. */
+
+  int currentSelectedRow = selectedRow();
+  int rowsCount = numberOfRows();
+  if (rowsCount <= 1 || currentSelectedRow < 1) {
+    return TableViewDataSource::indexFromCumulatedHeight(offsetY);
+  }
+
+  KDCoordinate currentCumulatedHeight = cumulatedHeightFromIndex(currentSelectedRow);
+  if (offsetY > currentCumulatedHeight) {
+    int iMax = min(k_memoizedCellHeightsCount/2 + 1, rowsCount - currentSelectedRow);
+    for (int i = 0; i < iMax; i++) {
+      currentCumulatedHeight+= rowHeight(currentSelectedRow + i);
+      if (offsetY <= currentCumulatedHeight) {
+        return currentSelectedRow + i;
+      }
+    }
+  } else {
+    int iMax = min(k_memoizedCellHeightsCount/2, currentSelectedRow);
+    for (int i = 1; i <= iMax; i++) {
+      currentCumulatedHeight-= rowHeight(currentSelectedRow-i);
+      if (offsetY > currentCumulatedHeight) {
+        return currentSelectedRow - i;
+      }
+    }
+  }
+  return TableViewDataSource::indexFromCumulatedHeight(offsetY);
+}
+
 int StorageFunctionListController::typeAtLocation(int i, int j) {
   if (isAddEmptyRow(j)){
     return i + 2;
diff --git a/apps/shared/storage_function_list_controller.h b/apps/shared/storage_function_list_controller.h
index c47644ad1..c8e21fb30 100644
--- a/apps/shared/storage_function_list_controller.h
+++ b/apps/shared/storage_function_list_controller.h
@@ -26,6 +26,7 @@ public:
   KDCoordinate cumulatedWidthFromIndex(int i) override;
   KDCoordinate cumulatedHeightFromIndex(int j) override;
   int indexFromCumulatedWidth(KDCoordinate offsetX) override;
+  int indexFromCumulatedHeight(KDCoordinate offsetY) override;
   int typeAtLocation(int i, int j) override;
   HighlightCell * reusableCell(int index, int type) override;
   int reusableCellCount(int type) override;
diff --git a/apps/solver/Makefile b/apps/solver/Makefile
index c010c0697..a15ab0b36 100644
--- a/apps/solver/Makefile
+++ b/apps/solver/Makefile
@@ -23,7 +23,5 @@ i18n_files += $(addprefix apps/solver/,\
 tests += $(addprefix apps/solver/test/,\
   equation_store.cpp\
 )
-test_objs += $(addprefix apps/solver/, equation.o equation_store.o)
-test_objs += $(addprefix apps/shared/, expression_model.o  expression_model_store.o)
 
 app_images += apps/solver/solver_icon.png
diff --git a/apps/statistics/Makefile b/apps/statistics/Makefile
index 003a98214..424fb48c0 100644
--- a/apps/statistics/Makefile
+++ b/apps/statistics/Makefile
@@ -34,6 +34,5 @@ i18n_files += $(addprefix apps/statistics/,\
 tests += $(addprefix apps/statistics/test/,\
   store.cpp\
 )
-test_objs += $(addprefix apps/statistics/, store.o)
 
 app_images += apps/statistics/stat_icon.png
diff --git a/escher/include/escher/app.h b/escher/include/escher/app.h
index ed164c7f4..15790005a 100644
--- a/escher/include/escher/app.h
+++ b/escher/include/escher/app.h
@@ -50,6 +50,9 @@ public:
   void setFirstResponder(Responder * responder);
   Responder * firstResponder();
   virtual bool processEvent(Ion::Events::Event event);
+  /* prepareForExit returns true if the app can be switched off in the current
+   * runloop step, else it prepares for a switch off and returns false. */
+  virtual bool prepareForExit() { return true; }
   void displayModalViewController(ViewController * vc, float verticalAlignment, float horizontalAlignment,
     KDCoordinate topMargin = 0, KDCoordinate leftMargin = 0, KDCoordinate bottomMargin = 0, KDCoordinate rightMargin = 0);
   void dismissModalViewController();
diff --git a/poincare/Makefile b/poincare/Makefile
index 532933cf4..4f5baca15 100644
--- a/poincare/Makefile
+++ b/poincare/Makefile
@@ -97,6 +97,7 @@ objs += $(addprefix poincare/src/,\
   nth_root.o\
   number.o\
   opposite.o\
+  parametered_expression_helper.o\
   parenthesis.o\
   permute_coefficient.o\
   power.o\
diff --git a/poincare/include/poincare/derivative.h b/poincare/include/poincare/derivative.h
index 9ae929760..3e2458f7f 100644
--- a/poincare/include/poincare/derivative.h
+++ b/poincare/include/poincare/derivative.h
@@ -22,6 +22,7 @@ public:
   // Properties
   Type type() const override { return Type::Derivative; }
   int polynomialDegree(Context & context, const char * symbolName) const override;
+  Expression replaceUnknown(const Symbol & symbol) override;
 
 private:
   // Layout
diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index aaca8f7bf..77a6a5fc4 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -14,6 +14,7 @@ namespace Poincare {
 
 class Context;
 class SymbolAbstract;
+class Symbol;
 
 class Expression : public TreeHandle {
   friend class AbsoluteValue;
@@ -154,6 +155,8 @@ public:
   static constexpr int k_maxNumberOfPolynomialCoefficients = k_maxPolynomialDegree+1;
   int getPolynomialReducedCoefficients(const char * symbolName, Expression coefficients[], Context & context, Preferences::AngleUnit angleUnit) const;
   Expression replaceSymbolWithExpression(const SymbolAbstract & symbol, const Expression & expression) { return node()->replaceSymbolWithExpression(symbol, expression); }
+  Expression replaceUnknown(const Symbol & symbol);
+  Expression defaultReplaceUnknown(const Symbol & symbol);
 
   /* Comparison */
   /* isIdenticalTo is the "easy" equality, it returns true if both trees have
@@ -167,7 +170,6 @@ public:
   int serialize(char * buffer, int bufferSize, Preferences::PrintFloatMode floatDisplayMode = Preferences::PrintFloatMode::Decimal, int numberOfSignificantDigits = PrintFloat::k_numberOfStoredSignificantDigits) const;
 
   /* Simplification */
-  static Expression ParseAndReduce(const char * text, Context & context, Preferences::AngleUnit);
   static Expression ParseAndSimplify(const char * text, Context & context, Preferences::AngleUnit angleUnit);
   Expression simplify(Context & context, Preferences::AngleUnit angleUnit);
   Expression reduce(Context & context, Preferences::AngleUnit angleUnit);
diff --git a/poincare/include/poincare/expression_node.h b/poincare/include/poincare/expression_node.h
index 82aa7677b..64d65bc67 100644
--- a/poincare/include/poincare/expression_node.h
+++ b/poincare/include/poincare/expression_node.h
@@ -13,6 +13,7 @@ namespace Poincare {
  * 'this' outdated. They should only be called in a wrapper on Expression. */
 
 class SymbolAbstract;
+class Symbol;
 
 class ExpressionNode : public TreeNode {
   friend class AdditionNode;
@@ -103,6 +104,7 @@ public:
   virtual Sign sign() const { return Sign::Unknown; }
   virtual bool isNumber() const { return false; }
   /*!*/ virtual Expression replaceSymbolWithExpression(const SymbolAbstract & symbol, const Expression & expression);
+  /*!*/ virtual Expression replaceUnknown(const Symbol & symbol);
   /*!*/ virtual Expression setSign(Sign s, Context & context, Preferences::AngleUnit angleUnit);
   virtual int polynomialDegree(Context & context, const char * symbolName) const;
   /*!*/ virtual int getPolynomialCoefficients(Context & context, const char * symbolName, Expression coefficients[]) const;
diff --git a/poincare/include/poincare/integral.h b/poincare/include/poincare/integral.h
index 2fc2cb42b..9c2f08dfa 100644
--- a/poincare/include/poincare/integral.h
+++ b/poincare/include/poincare/integral.h
@@ -21,6 +21,8 @@ public:
   // ExpressionNode
   Type type() const override { return Type::Integral; }
   int polynomialDegree(Context & context, const char * symbolName) const override;
+  Expression replaceUnknown(const Symbol & symbol) override;
+
 private:
   // Layout
   Layout createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
diff --git a/poincare/include/poincare/parametered_expression_helper.h b/poincare/include/poincare/parametered_expression_helper.h
new file mode 100644
index 000000000..d56888026
--- /dev/null
+++ b/poincare/include/poincare/parametered_expression_helper.h
@@ -0,0 +1,28 @@
+#ifndef POINCARE_PARAMETERED_EXPRESSION_HELPER_H
+#define POINCARE_PARAMETERED_EXPRESSION_HELPER_H
+
+#include <poincare/expression.h>
+
+namespace Poincare {
+
+class SymbolAbstract;
+class Symbol;
+
+// Parametered expressions are Integral, Derivative, Sum and Product.
+
+namespace ParameteredExpressionHelper {
+  /* We sometimes replace 'x' by 'UnknownX' to differentiate between a variable
+   * and a function parameter. For instance, when defining the function
+   * f(x)=cos(x) in Graph, we want x to be an unknown, instead of having f be
+   * the constant function equal to cos(user variable that is named x).
+   *
+   * In parametered expression, we do not want to replace all the 'x' with
+   * unknowns: for instance, we want to change f(x)=diff(cos(x),x,x) into
+   * f(X)=diff(cos(x),x,X), X being an unknown. ReplaceUnknownInExpression does
+   * that. */
+  Expression ReplaceUnknownInExpression(Expression e, const Symbol & symbolToReplace);
+};
+
+}
+
+#endif
diff --git a/poincare/include/poincare/product.h b/poincare/include/poincare/product.h
index 76e2fe4d2..fd98fa751 100644
--- a/poincare/include/poincare/product.h
+++ b/poincare/include/poincare/product.h
@@ -16,6 +16,8 @@ public:
 #endif
 
   Type type() const override { return Type::Product; }
+  Expression replaceUnknown(const Symbol & symbol) override;
+
 private:
   float emptySequenceValue() const override { return 1.0f; }
   Layout createSequenceLayout(Layout argumentLayout, Layout symbolLayout, Layout subscriptLayout, Layout superscriptLayout) const override;
diff --git a/poincare/include/poincare/sum.h b/poincare/include/poincare/sum.h
index e39cffcd3..0ac12d2b1 100644
--- a/poincare/include/poincare/sum.h
+++ b/poincare/include/poincare/sum.h
@@ -16,6 +16,8 @@ public:
 #endif
 
   Type type() const override { return Type::Sum; }
+  Expression replaceUnknown(const Symbol & symbol) override;
+
 private:
   float emptySequenceValue() const override { return 0.0f; }
   Layout createSequenceLayout(Layout argumentLayout, Layout symbolLayout, Layout subscriptLayout, Layout superscriptLayout) const override;
diff --git a/poincare/include/poincare/symbol.h b/poincare/include/poincare/symbol.h
index b7d1715c0..eb6a90389 100644
--- a/poincare/include/poincare/symbol.h
+++ b/poincare/include/poincare/symbol.h
@@ -20,6 +20,7 @@ public:
   // Expression Properties
   Type type() const override { return Type::Symbol; }
   Expression replaceSymbolWithExpression(const SymbolAbstract & symbol, const Expression & expression) override;
+  Expression replaceUnknown(const Symbol & symbol) override;
   int polynomialDegree(Context & context, const char * symbolName) const override;
   int getPolynomialCoefficients(Context & context, const char * symbolName, Expression coefficients[]) const override;
   int getVariables(Context & context, isVariableTest isVariable, char * variables, int maxSizeVariable) const override;
@@ -77,6 +78,7 @@ public:
   // Expression
   Expression shallowReduce(Context & context, Preferences::AngleUnit angleUnit, ExpressionNode::ReductionTarget target);
   Expression replaceSymbolWithExpression(const SymbolAbstract & symbol, const Expression & expression);
+  Expression replaceUnknown(const Symbol & symbol);
   int getPolynomialCoefficients(Context & context, const char * symbolName, Expression coefficients[]) const;
   Expression shallowReplaceReplaceableSymbols(Context & context);
 private:
diff --git a/poincare/src/derivative.cpp b/poincare/src/derivative.cpp
index 38e0b16c6..33ac1b490 100644
--- a/poincare/src/derivative.cpp
+++ b/poincare/src/derivative.cpp
@@ -1,8 +1,9 @@
 #include <poincare/derivative.h>
-#include <poincare/symbol.h>
 #include <poincare/layout_helper.h>
+#include <poincare/parametered_expression_helper.h>
 #include <poincare/serialization_helper.h>
 #include <poincare/simplification_helper.h>
+#include <poincare/symbol.h>
 #include <poincare/undefined.h>
 #include <cmath>
 #include <assert.h>
@@ -26,6 +27,10 @@ int DerivativeNode::polynomialDegree(Context & context, const char * symbolName)
   return ExpressionNode::polynomialDegree(context, symbolName);
 }
 
+Expression DerivativeNode::replaceUnknown(const Symbol & symbol) {
+  return ParameteredExpressionHelper::ReplaceUnknownInExpression(Derivative(this), symbol);
+}
+
 Layout DerivativeNode::createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
   return LayoutHelper::Prefix(this, floatDisplayMode, numberOfSignificantDigits, Derivative::s_functionHelper.name());
 }
diff --git a/poincare/src/expression.cpp b/poincare/src/expression.cpp
index 1363d40de..99a630389 100644
--- a/poincare/src/expression.cpp
+++ b/poincare/src/expression.cpp
@@ -281,6 +281,18 @@ int Expression::getPolynomialReducedCoefficients(const char * symbolName, Expres
   return degree;
 }
 
+Expression Expression::replaceUnknown(const Symbol & symbol) {
+  return node()->replaceUnknown(symbol);
+}
+
+Expression Expression::defaultReplaceUnknown(const Symbol & symbol) {
+  int nbChildren = numberOfChildren();
+  for (int i = 0; i < nbChildren; i++) {
+    childAtIndex(i).replaceUnknown(symbol);
+  }
+  return *this;
+}
+
 /* Comparison */
 
 bool Expression::isIdenticalTo(const Expression e) const {
@@ -312,14 +324,6 @@ int Expression::serialize(char * buffer, int bufferSize, Preferences::PrintFloat
 
 /* Simplification */
 
-Expression Expression::ParseAndReduce(const char * text, Context & context, Preferences::AngleUnit angleUnit) {
-  Expression exp = Parse(text);
-  if (exp.isUninitialized()) {
-    return Undefined();
-  }
-  return exp.reduce(context, angleUnit);
-}
-
 Expression Expression::ParseAndSimplify(const char * text, Context & context, Preferences::AngleUnit angleUnit) {
   Expression exp = Parse(text);
   if (exp.isUninitialized()) {
@@ -423,7 +427,7 @@ U Expression::approximateToScalar(Context& context, Preferences::AngleUnit angle
 
 template<typename U>
 U Expression::approximateToScalar(const char * text, Context& context, Preferences::AngleUnit angleUnit) {
-  Expression exp = ParseAndReduce(text, context, angleUnit);
+  Expression exp = ParseAndSimplify(text, context, angleUnit);
   return exp.approximateToScalar<U>(context, angleUnit);
 }
 
diff --git a/poincare/src/expression_node.cpp b/poincare/src/expression_node.cpp
index f0c2f61b5..446b7caa5 100644
--- a/poincare/src/expression_node.cpp
+++ b/poincare/src/expression_node.cpp
@@ -9,6 +9,10 @@ Expression ExpressionNode::replaceSymbolWithExpression(const SymbolAbstract & sy
   return Expression(this).defaultReplaceSymbolWithExpression(symbol, expression);
 }
 
+Expression ExpressionNode::replaceUnknown(const Symbol & symbol) {
+  return Expression(this).defaultReplaceUnknown(symbol);
+}
+
 Expression ExpressionNode::setSign(Sign s, Context & context, Preferences::AngleUnit angleUnit) {
   assert(false);
   return Expression();
diff --git a/poincare/src/integer.cpp b/poincare/src/integer.cpp
index 5b5e1a96c..d69cd9617 100644
--- a/poincare/src/integer.cpp
+++ b/poincare/src/integer.cpp
@@ -323,7 +323,7 @@ T Integer::approximate() const {
   */
 
   if (isInfinity()) {
-    return INFINITY;
+    return m_negative ? -INFINITY : INFINITY;
   }
 
   native_uint_t lastDigit = m_numberOfDigits > 0 ? digit(m_numberOfDigits-1) : 0;
@@ -334,7 +334,7 @@ T Integer::approximate() const {
   /* Escape case if the exponent is too big to be stored */
   assert(m_numberOfDigits > 0);
   if (((int)m_numberOfDigits-1)*32+numberOfBitsInLastDigit-1> IEEE754<T>::maxExponent()-IEEE754<T>::exponentOffset()) {
-    return INFINITY;
+    return  m_negative ? -INFINITY : INFINITY;
   }
   exponent += (m_numberOfDigits-1)*32;
   exponent += numberOfBitsInLastDigit-1;
diff --git a/poincare/src/integral.cpp b/poincare/src/integral.cpp
index e4a001ddc..0c2c26fd5 100644
--- a/poincare/src/integral.cpp
+++ b/poincare/src/integral.cpp
@@ -1,6 +1,7 @@
 #include <poincare/integral.h>
 #include <poincare/complex.h>
 #include <poincare/integral_layout.h>
+#include <poincare/parametered_expression_helper.h>
 #include <poincare/serialization_helper.h>
 #include <poincare/symbol.h>
 #include <poincare/undefined.h>
@@ -26,6 +27,10 @@ int IntegralNode::polynomialDegree(Context & context, const char * symbolName) c
   return ExpressionNode::polynomialDegree(context, symbolName);
 }
 
+Expression IntegralNode::replaceUnknown(const Symbol & symbol) {
+  return ParameteredExpressionHelper::ReplaceUnknownInExpression(Integral(this), symbol);
+}
+
 Layout IntegralNode::createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
   return IntegralLayout(
       childAtIndex(0)->createLayout(floatDisplayMode, numberOfSignificantDigits),
diff --git a/poincare/src/parametered_expression_helper.cpp b/poincare/src/parametered_expression_helper.cpp
new file mode 100644
index 000000000..944003c16
--- /dev/null
+++ b/poincare/src/parametered_expression_helper.cpp
@@ -0,0 +1,33 @@
+#include <poincare/parametered_expression_helper.h>
+#include <poincare/symbol.h>
+#include <string.h>
+#include <assert.h>
+
+namespace Poincare {
+
+Expression ParameteredExpressionHelper::ReplaceUnknownInExpression(Expression e, const Symbol & symbolToReplace) {
+  assert(!e.isUninitialized());
+  assert(e.type() == ExpressionNode::Type::Integral
+      || e.type() == ExpressionNode::Type::Derivative
+      || e.type() == ExpressionNode::Type::Sum
+      || e.type() == ExpressionNode::Type::Product);
+  assert(!symbolToReplace.isUninitialized());
+  assert(symbolToReplace.type() == ExpressionNode::Type::Symbol);
+
+  int numberOfChildren = e.numberOfChildren();
+  assert(numberOfChildren > 2);
+
+  Expression child1 = e.childAtIndex(1);
+  assert(child1.type() == ExpressionNode::Type::Symbol);
+
+  Symbol& parameterChild = static_cast<Symbol &>(child1);
+  if (strcmp(parameterChild.name(), symbolToReplace.name()) != 0) {
+    return e.defaultReplaceUnknown(symbolToReplace);
+  }
+  for (int i = 2; i < numberOfChildren; i++) {
+    e.childAtIndex(i).replaceUnknown(symbolToReplace);
+  }
+  return e;
+}
+
+}
diff --git a/poincare/src/product.cpp b/poincare/src/product.cpp
index d5dd1ce27..721c64648 100644
--- a/poincare/src/product.cpp
+++ b/poincare/src/product.cpp
@@ -1,5 +1,6 @@
 #include <poincare/product.h>
 #include <poincare/multiplication.h>
+#include <poincare/parametered_expression_helper.h>
 #include <poincare/product_layout.h>
 #include <poincare/layout_helper.h>
 #include <poincare/serialization_helper.h>
@@ -13,6 +14,10 @@ namespace Poincare {
 
 constexpr Expression::FunctionHelper Product::s_functionHelper;
 
+Expression ProductNode::replaceUnknown(const Symbol & symbol) {
+  return ParameteredExpressionHelper::ReplaceUnknownInExpression(Product(this), symbol);
+}
+
 Layout ProductNode::createSequenceLayout(Layout argumentLayout, Layout symbolLayout, Layout subscriptLayout, Layout superscriptLayout) const {
   return ProductLayout(argumentLayout, symbolLayout, subscriptLayout, superscriptLayout);
 }
diff --git a/poincare/src/sum.cpp b/poincare/src/sum.cpp
index c7bd4f496..9f35641bd 100644
--- a/poincare/src/sum.cpp
+++ b/poincare/src/sum.cpp
@@ -2,6 +2,7 @@
 #include <poincare/addition.h>
 #include <poincare/sum_layout.h>
 #include <poincare/layout_helper.h>
+#include <poincare/parametered_expression_helper.h>
 #include <poincare/serialization_helper.h>
 extern "C" {
 #include <assert.h>
@@ -13,6 +14,10 @@ namespace Poincare {
 
 constexpr Expression::FunctionHelper Sum::s_functionHelper;
 
+Expression SumNode::replaceUnknown(const Symbol & symbol) {
+  return ParameteredExpressionHelper::ReplaceUnknownInExpression(Sum(this), symbol);
+}
+
 Layout SumNode::createSequenceLayout(Layout argumentLayout, Layout symbolLayout, Layout subscriptLayout, Layout superscriptLayout) const {
   return SumLayout(argumentLayout, symbolLayout, subscriptLayout, superscriptLayout);
 }
diff --git a/poincare/src/symbol.cpp b/poincare/src/symbol.cpp
index 47f2c4aed..dc9ecf035 100644
--- a/poincare/src/symbol.cpp
+++ b/poincare/src/symbol.cpp
@@ -27,6 +27,10 @@ Expression SymbolNode::replaceSymbolWithExpression(const SymbolAbstract & symbol
   return Symbol(this).replaceSymbolWithExpression(symbol, expression);
 }
 
+Expression SymbolNode::replaceUnknown(const Symbol & symbol) {
+  return Symbol(this).replaceUnknown(symbol);
+}
+
 int SymbolNode::polynomialDegree(Context & context, const char * symbolName) const {
   if (strcmp(m_name,symbolName) == 0) {
     return 1;
@@ -180,6 +184,12 @@ Expression Symbol::replaceSymbolWithExpression(const SymbolAbstract & symbol, co
   return *this;
 }
 
+Expression Symbol::replaceUnknown(const Symbol & symbol) {
+  assert(!symbol.isUninitialized());
+  assert(symbol.type() == ExpressionNode::Type::Symbol);
+  return replaceSymbolWithExpression(symbol, Symbol(SpecialSymbols::UnknownX));
+}
+
 int Symbol::getPolynomialCoefficients(Context & context, const char * symbolName, Expression coefficients[]) const {
   if (strcmp(name(), symbolName) == 0) {
     coefficients[0] = Rational(0);