diff --git a/apps/calculation/app.cpp b/apps/calculation/app.cpp
index 51b521e66..2d9e56937 100644
--- a/apps/calculation/app.cpp
+++ b/apps/calculation/app.cpp
@@ -92,7 +92,7 @@ bool App::textInputIsCorrect(const char * text) {
    * less than k_printedExpressionLength characters. Otherwise, we prevent the
    * user from adding this expression to the calculation store. */
   Expression exp = Expression::parse(text);
-  if (!exp.isDefined()) {
+  if (exp.isUninitialized()) {
     return false;
   }
   exp = exp.replaceSymbolWithExpression(Symbol::SpecialSymbols::Ans, static_cast<Snapshot *>(snapshot())->calculationStore()->ansExpression(localContext()));
diff --git a/apps/calculation/calculation.cpp b/apps/calculation/calculation.cpp
index 2b9cf58ed..ecf6bc65d 100644
--- a/apps/calculation/calculation.cpp
+++ b/apps/calculation/calculation.cpp
@@ -100,7 +100,7 @@ const char * Calculation::approximateOutputText() {
 }
 
 Expression Calculation::input() {
-  if (!m_input.isDefined()) {
+  if (m_input.isUninitialized()) {
     m_input = Expression::parse(m_inputText);
   }
   return m_input;
@@ -143,13 +143,13 @@ void Calculation::tidy() {
 }
 
 Expression Calculation::exactOutput(Context * context) {
-  if (!m_exactOutput.isDefined()) {
+  if (m_exactOutput.isUninitialized()) {
     /* Because the angle unit might have changed, we do not simplify again. We
      * thereby avoid turning cos(Pi/4) into sqrt(2)/2 and displaying
      * 'sqrt(2)/2 = 0.999906' (which is totally wrong) instead of
      * 'cos(pi/4) = 0.999906' (which is true in degree). */
     m_exactOutput = Expression::parse(m_exactOutputText);
-    if (!m_exactOutput.isDefined()) {
+    if (m_exactOutput.isUninitialized()) {
       m_exactOutput = Undefined();
     }
   }
@@ -161,7 +161,7 @@ LayoutRef Calculation::createExactOutputLayout(Context * context) {
 }
 
 Expression Calculation::approximateOutput(Context * context) {
-  if (!m_approximateOutput.isDefined()) {
+  if (m_approximateOutput.isUninitialized()) {
     /* To ensure that the expression 'm_output' is a matrix or a complex, we
      * call 'evaluate'. */
     Expression exp = Expression::parse(m_approximateOutputText);
diff --git a/apps/calculation/edit_expression_controller.cpp b/apps/calculation/edit_expression_controller.cpp
index 04b8ca42f..49ffeff8d 100644
--- a/apps/calculation/edit_expression_controller.cpp
+++ b/apps/calculation/edit_expression_controller.cpp
@@ -154,11 +154,10 @@ bool EditExpressionController::inputViewDidReceiveEvent(Ion::Events::Event event
 
 bool EditExpressionController::inputViewDidFinishEditing(const char * text, LayoutRef layoutR) {
   App * calculationApp = (App *)app();
-  if (!layoutR.isDefined()) {
+  if (layoutR.isUninitialized()) {
     assert(text);
     strlcpy(m_cacheBuffer, text, Calculation::k_printedExpressionSize);
   } else {
-    assert(layoutR.isDefined());
     layoutR.serialize(m_cacheBuffer, Calculation::k_printedExpressionSize);
   }
   m_calculationStore->push(m_cacheBuffer, calculationApp->localContext());
diff --git a/apps/calculation/history_view_cell.cpp b/apps/calculation/history_view_cell.cpp
index 21bd7f2f8..c1a0cd5df 100644
--- a/apps/calculation/history_view_cell.cpp
+++ b/apps/calculation/history_view_cell.cpp
@@ -100,7 +100,7 @@ void HistoryViewCell::setCalculation(Calculation * calculation) {
   /* Both output expressions have to be updated at the same time. Otherwise,
    * when updating one layout, if the second one still points to a deleted
    * layout, calling to layoutSubviews() would fail. */
-  if (m_exactOutputLayout.isDefined()) {
+  if (!m_exactOutputLayout.isUninitialized()) {
     m_exactOutputLayout = Poincare::LayoutRef();
   }
   if (!calculation->shouldOnlyDisplayApproximateOutput(calculationApp->localContext())) {
diff --git a/apps/shared/expression_field_delegate_app.cpp b/apps/shared/expression_field_delegate_app.cpp
index 46d6b96ec..6e4b377e1 100644
--- a/apps/shared/expression_field_delegate_app.cpp
+++ b/apps/shared/expression_field_delegate_app.cpp
@@ -41,7 +41,7 @@ bool ExpressionFieldDelegateApp::layoutFieldDidReceiveEvent(LayoutField * layout
       displayWarning(I18n::Message::SyntaxError);
       return true;
     }
-    if (!exp.isDefined()) {
+    if (exp.isUninitialized()) {
       layoutField->app()->displayWarning(I18n::Message::SyntaxError);
       return true;
     }
diff --git a/apps/shared/expression_model.cpp b/apps/shared/expression_model.cpp
index 984ce6e85..b59693407 100644
--- a/apps/shared/expression_model.cpp
+++ b/apps/shared/expression_model.cpp
@@ -20,14 +20,14 @@ const char * ExpressionModel::text() const {
 }
 
 Poincare::Expression ExpressionModel::expression(Poincare::Context * context) const {
-  if (!m_expression.isDefined()) {
+  if (m_expression.isUninitialized()) {
     m_expression = PoincareHelpers::ParseAndSimplify(m_text, *context);
   }
   return m_expression;
 }
 
 LayoutRef ExpressionModel::layoutRef() {
-  if (!m_layoutRef.isDefined()) {
+  if (m_layoutRef.isUninitialized()) {
     Expression nonSimplifiedExpression = Expression::parse(m_text);
     m_layoutRef = PoincareHelpers::CreateLayout(nonSimplifiedExpression);
   }
@@ -49,7 +49,7 @@ void ExpressionModel::setContent(const char * c) {
    * the m_layout and m_expression. */
 // TODO: the previous expression and layout are going to be destroyed as soon as we call expression(). Should we optimize this?
 #if 0
-  if (m_layoutRef.isDefined()) {
+  if (!m_layoutRef.isUninitialized()) {
     m_layoutRef = LayoutRef();
   }
   if (m_expression != nullptr) {
@@ -66,7 +66,7 @@ void ExpressionModel::tidy() {
   m_expression = Expression(); ?
 
 
-  if (m_layoutRef.isDefined()) {
+  if (!m_layoutRef.isUninitialized()) {
     m_layoutRef = LayoutRef();
   }
   if (m_expression != nullptr) {
diff --git a/apps/shared/expression_model_list_controller.cpp b/apps/shared/expression_model_list_controller.cpp
index 0cda0150a..aa8a2a4e9 100644
--- a/apps/shared/expression_model_list_controller.cpp
+++ b/apps/shared/expression_model_list_controller.cpp
@@ -23,7 +23,7 @@ KDCoordinate ExpressionModelListController::expressionRowHeight(int j) {
     return Metric::StoreRowHeight;
   }
   ExpressionModel * m = modelStore()->modelAtIndex(j);
-  if (!m->layoutRef().isDefined()) {
+  if (m->layoutRef().isUninitialized()) {
     return Metric::StoreRowHeight;
   }
   KDCoordinate modelSize = m->layoutRef().layoutSize().height();
diff --git a/apps/shared/expression_model_store.cpp b/apps/shared/expression_model_store.cpp
index 02e98fba6..970a287b1 100644
--- a/apps/shared/expression_model_store.cpp
+++ b/apps/shared/expression_model_store.cpp
@@ -39,7 +39,7 @@ ExpressionModel * ExpressionModelStore::definedModelAtIndex(int i) {
   assert(i>=0 && i<m_numberOfModels);
   int index = 0;
   for (int k = 0; k < m_numberOfModels; k++) {
-    if (modelAtIndex(k)->isDefined()) {
+    if (!modelAtIndex(k)->isUninitialized()) {
       if (i == index) {
         return modelAtIndex(k);
       }
@@ -53,7 +53,7 @@ ExpressionModel * ExpressionModelStore::definedModelAtIndex(int i) {
 int ExpressionModelStore::numberOfDefinedModels() {
   int result = 0;
   for (int i = 0; i < m_numberOfModels; i++) {
-    if (modelAtIndex(i)->isDefined()) {
+    if (!modelAtIndex(i)->isUninitialized()) {
       result++;
     }
   }
diff --git a/apps/shared/scrollable_exact_approximate_expressions_view.cpp b/apps/shared/scrollable_exact_approximate_expressions_view.cpp
index 8276592b3..1cb08e3d9 100644
--- a/apps/shared/scrollable_exact_approximate_expressions_view.cpp
+++ b/apps/shared/scrollable_exact_approximate_expressions_view.cpp
@@ -70,10 +70,10 @@ Poincare::LayoutRef ScrollableExactApproximateExpressionsView::ContentCell::layo
 }
 
 int ScrollableExactApproximateExpressionsView::ContentCell::numberOfSubviews() const {
-  if (m_exactExpressionView.layoutRef().isDefined()) {
-    return 3;
+  if (m_exactExpressionView.layoutRef().isUninitialized()) {
+    return 1;
   }
-  return 1;
+  return 3;
 }
 
 View * ScrollableExactApproximateExpressionsView::ContentCell::subviewAtIndex(int index) {
@@ -115,7 +115,7 @@ void ScrollableExactApproximateExpressionsView::setEqualMessage(I18n::Message eq
 }
 
 void ScrollableExactApproximateExpressionsView::didBecomeFirstResponder() {
-  if (!m_contentCell.exactExpressionView()->layoutRef().isDefined()) {
+  if (m_contentCell.exactExpressionView()->layoutRef().isUninitialized()) {
     setSelectedSubviewType(SubviewType::ApproximativeOutput);
   } else {
     setSelectedSubviewType(SubviewType::ExactOutput);
diff --git a/apps/shared/store_controller.cpp b/apps/shared/store_controller.cpp
index d7094ed5a..f8074d99c 100644
--- a/apps/shared/store_controller.cpp
+++ b/apps/shared/store_controller.cpp
@@ -73,7 +73,7 @@ bool StoreController::textFieldDidFinishEditing(TextField * textField, const cha
   if (textField == contentView()->formulaInputView()->textField()) {
     // Handle formula input
     Expression expression = Expression::parse(textField->text());
-    if (!expression.isDefined()) {
+    if (expression.isUninitialized()) {
       app()->displayWarning(I18n::Message::SyntaxError);
       return false;
     }
diff --git a/apps/shared/text_field_delegate_app.cpp b/apps/shared/text_field_delegate_app.cpp
index 0fef4e5d3..2a9d3896f 100644
--- a/apps/shared/text_field_delegate_app.cpp
+++ b/apps/shared/text_field_delegate_app.cpp
@@ -79,7 +79,7 @@ bool TextFieldDelegateApp::textFieldShouldFinishEditing(TextField * textField, I
 bool TextFieldDelegateApp::textFieldDidReceiveEvent(TextField * textField, Ion::Events::Event event) {
   if (textField->isEditing() && textField->textFieldShouldFinishEditing(event)) {
     Expression exp = Expression::parse(textField->text());
-    if (!exp.isDefined()) {
+    if (exp.isUninitialized()) {
       textField->app()->displayWarning(I18n::Message::SyntaxError);
       return true;
     }
diff --git a/apps/variable_box_controller.cpp b/apps/variable_box_controller.cpp
index 1218a07bc..942c5e1c9 100644
--- a/apps/variable_box_controller.cpp
+++ b/apps/variable_box_controller.cpp
@@ -147,7 +147,7 @@ void VariableBoxController::ContentViewController::willDisplayCellForIndex(Highl
     return;
   }
   myCell->displayExpression(true);
-  if (evaluation.isDefined()) {
+  if (!evaluation.isUninitialized()) {
     /* TODO: implement list contexts */
     // TODO: handle matrix and scalar!
     LayoutRef layoutR = layoutRefForIndex(index);
@@ -169,7 +169,7 @@ KDCoordinate VariableBoxController::ContentViewController::rowHeight(int index)
     return Metric::ToolboxRowHeight;
   }
   LayoutRef layoutR = layoutRefForIndex(index);
-  if (layoutR.isDefined()) {
+  if (!layoutR.isUninitialized()) {
     return layoutR.layoutSize().height()+k_leafMargin;
   }
   return Metric::ToolboxRowHeight;
diff --git a/escher/src/expression_view.cpp b/escher/src/expression_view.cpp
index e716cebcf..e55fa4582 100644
--- a/escher/src/expression_view.cpp
+++ b/escher/src/expression_view.cpp
@@ -42,7 +42,7 @@ int ExpressionView::numberOfLayouts() const {
 }
 
 KDSize ExpressionView::minimalSizeForOptimalDisplay() const {
-  if (!m_layoutRef.isDefined()) {
+  if (m_layoutRef.isUninitialized()) {
     return KDSizeZero;
   }
   KDSize expressionSize = m_layoutRef.layoutSize();
@@ -60,7 +60,7 @@ KDPoint ExpressionView::absoluteDrawingOrigin() const {
 
 void ExpressionView::drawRect(KDContext * ctx, KDRect rect) const {
   ctx->fillRect(rect, m_backgroundColor);
-  if (m_layoutRef.isDefined()) {
+  if (!m_layoutRef.isUninitialized()) {
     m_layoutRef.draw(ctx, drawingOrigin(), m_textColor, m_backgroundColor);
   }
 }
diff --git a/escher/src/layout_field.cpp b/escher/src/layout_field.cpp
index 8e580d75a..1f5d80dd2 100644
--- a/escher/src/layout_field.cpp
+++ b/escher/src/layout_field.cpp
@@ -79,7 +79,7 @@ bool LayoutField::handleEventWithText(const char * text, bool indentation, bool
     m_contentView.cursor()->addEmptyMatrixLayout();
   } else {
     Expression resultExpression = Expression::parse(text);
-    if (!resultExpression.isDefined()) {
+    if (resultExpression.isUninitialized()) {
       m_contentView.cursor()->insertText(text);
     } else {
       LayoutRef resultLayoutRef = resultExpression.createLayout(Poincare::Preferences::sharedPreferences()->displayMode(), Poincare::Preferences::sharedPreferences()->numberOfSignificantDigits());
@@ -248,7 +248,7 @@ void LayoutField::scrollToBaselinedRect(KDRect rect, KDCoordinate baseline) {
 }
 
 void LayoutField::insertLayoutAtCursor(LayoutRef layoutR, LayoutRef pointedLayoutR, bool forceCursorRightOfLayout) {
-  if (!layoutR.isDefined() || layoutRef().isAllocationFailure()) {
+  if (layoutR.isUninitialized() || layoutRef().isAllocationFailure()) {
     return;
   }
 
@@ -265,7 +265,7 @@ void LayoutField::insertLayoutAtCursor(LayoutRef layoutR, LayoutRef pointedLayou
   if (layoutRef().isAllocationFailure()) {
     m_contentView.cursor()->setLayoutReference(layoutRef());
   } else if(!forceCursorRightOfLayout) {
-    if (pointedLayoutR.isDefined() && (!layoutWillBeMerged || pointedLayoutR != layoutR)) {
+    if (!pointedLayoutR.isUninitialized() && (!layoutWillBeMerged || pointedLayoutR != layoutR)) {
       // Make sure the layout was inserted (its parent is not uninitialized)
       m_contentView.cursor()->setLayoutReference(pointedLayoutR);
       m_contentView.cursor()->setPosition(LayoutCursor::Position::Right);
@@ -292,7 +292,7 @@ void LayoutField::insertLayoutAtCursor(LayoutRef layoutR, LayoutRef pointedLayou
   if (!layoutWillBeMerged) {
     scrollRightOfLayout(layoutR);
   } else {
-    assert(lastMergedLayoutChild.isDefined());
+    assert(!lastMergedLayoutChild.isUninitialized());
     scrollRightOfLayout(lastMergedLayoutChild);
   }
   scrollToCursor();
diff --git a/escher/src/selectable_table_view.cpp b/escher/src/selectable_table_view.cpp
index 54f486318..e5525220d 100644
--- a/escher/src/selectable_table_view.cpp
+++ b/escher/src/selectable_table_view.cpp
@@ -129,7 +129,7 @@ bool SelectableTableView::handleEvent(Ion::Events::Event event) {
       return true;
     }
     Poincare::LayoutRef layoutR = cell->layoutRef();
-    if (layoutR.isDefined() && !layoutR.isAllocationFailure()) {
+    if (!layoutR.isUninitialized() && !layoutR.isAllocationFailure()) {
       Clipboard::sharedClipboard()->store(layoutR);
       return true;
     }
diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index 0e31c36c1..e7b200245 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -108,7 +108,7 @@ public:
   bool isEqualToItsApproximationLayout(Expression approximation, int bufferSize, Preferences::AngleUnit angleUnit, Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits, Context & context);
 
   /* Layout Helper */
-  LayoutRef createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const { return isDefined() ? node()->createLayout(floatDisplayMode, numberOfSignificantDigits) : LayoutRef(); }
+  LayoutRef createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const { return node()->createLayout(floatDisplayMode, numberOfSignificantDigits); }
   int serialize(char * buffer, int bufferSize, Preferences::PrintFloatMode floatDisplayMode = Preferences::PrintFloatMode::Decimal, int numberOfSignificantDigits = PrintFloat::k_numberOfStoredSignificantDigits) const { return this->node()->serialize(buffer, bufferSize, floatDisplayMode, numberOfSignificantDigits); }
 
   /* Simplification */
diff --git a/poincare/include/poincare/layout_cursor.h b/poincare/include/poincare/layout_cursor.h
index d82a32739..67989e0df 100644
--- a/poincare/include/poincare/layout_cursor.h
+++ b/poincare/include/poincare/layout_cursor.h
@@ -48,7 +48,7 @@ public:
   }
 
   // Definition
-  bool isDefined() const { return m_layoutRef.isDefined(); }
+  bool isDefined() const { return !m_layoutRef.isUninitialized(); }
 
   // Getters and setters
   LayoutRef layoutReference() { return m_layoutRef; }
diff --git a/poincare/include/poincare/layout_reference.h b/poincare/include/poincare/layout_reference.h
index 554e8302b..ad528ad2f 100644
--- a/poincare/include/poincare/layout_reference.h
+++ b/poincare/include/poincare/layout_reference.h
@@ -92,7 +92,7 @@ public:
   void replaceChildWithEmpty(LayoutReference oldChild, LayoutCursor * cursor = nullptr);
   void replaceWith(LayoutReference newChild, LayoutCursor * cursor) {
     LayoutReference p = parent();
-    assert(p.isDefined());
+    assert(!p.isUninitialized());
     p.replaceChild(*this, newChild, cursor);
   }
   void replaceWithJuxtapositionOf(LayoutReference leftChild, LayoutReference rightChild, LayoutCursor * cursor, bool putCursorInTheMiddle = false);
diff --git a/poincare/include/poincare/tree_by_reference.h b/poincare/include/poincare/tree_by_reference.h
index 704225733..5e7586351 100644
--- a/poincare/include/poincare/tree_by_reference.h
+++ b/poincare/include/poincare/tree_by_reference.h
@@ -38,53 +38,54 @@ public:
   int identifier() const { return m_identifier; }
   virtual TreeNode * node() const { return TreePool::sharedPool()->node(m_identifier); }
 
-  bool isDefined() const { return m_identifier != TreePool::NoNodeIdentifier && node() != nullptr; }
-  bool isAllocationFailure() const { return isDefined() && node()->isAllocationFailure(); }
+  bool isUninitialized() const { return node()->isUninitialized(); }
+  bool isAllocationFailure() const { return node()->isAllocationFailure(); }
+  bool isStatic() const { return node()->isStatic(); }
 
   int nodeRetainCount() const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->retainCount();
   }
   void incrementNumberOfChildren(int increment = 1) {
-    assert(isDefined());
+    assert(!isUninitialized());
     node()->incrementNumberOfChildren(increment);
   }
   void decrementNumberOfChildren(int decrement = 1) {
-    assert(isDefined());
+    assert(!isUninitialized());
     node()->decrementNumberOfChildren(decrement);
   }
   int numberOfDescendants(bool includeSelf) const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->numberOfDescendants(includeSelf);
   }
 
   /* Hierarchy */
   bool hasChild(TreeByReference t) const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->hasChild(t.node());
   }
   bool hasSibling(TreeByReference t) const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->hasSibling(t.node());
   }
   bool hasAncestor(TreeByReference t, bool includeSelf) const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->hasAncestor(t.node(), includeSelf);
   }
   int numberOfChildren() const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->numberOfChildren();
   }
   TreeByReference parent() const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return TreeByReference(node()->parent());
   }
   TreeByReference childAtIndex(int i) const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return TreeByReference(node()->childAtIndex(i));
   }
   int indexOfChild(TreeByReference t) const {
-    assert(isDefined());
+    assert(!isUninitialized());
     return node()->indexOfChild(t.node());
   }
 
@@ -118,9 +119,7 @@ protected:
   TreeByReference() : m_identifier(-1) {}
   void setIdentifierAndRetain(int newId) {
     m_identifier = newId;
-    if (isDefined()) {
-      node()->retain();
-    }
+    node()->retain();
   }
   void setTo(const TreeByReference & tr);
   /* Hierarchy operations */
diff --git a/poincare/include/poincare/tree_by_value.h b/poincare/include/poincare/tree_by_value.h
index 2cebd70fe..bde69351c 100644
--- a/poincare/include/poincare/tree_by_value.h
+++ b/poincare/include/poincare/tree_by_value.h
@@ -19,7 +19,7 @@ public:
 
   virtual ~TreeByValue() = default;
 
-  bool isDefined() const { return TreeByReference::isDefined(); }
+  bool isUninitialized() const { return TreeByReference::isUninitialized(); }
   bool isAllocationFailure() const { return TreeByReference::isAllocationFailure(); }
 
   TreeNode * node() const override { return TreeByReference::node(); }
diff --git a/poincare/src/addition.cpp b/poincare/src/addition.cpp
index 75e34af7d..a27e9332f 100644
--- a/poincare/src/addition.cpp
+++ b/poincare/src/addition.cpp
@@ -75,7 +75,7 @@ Expression AdditionNode::factorizeOnCommonDenominator(Context & context, Prefere
   Multiplication commonDenominator = Multiplication();
   for (int i = 0; i < numberOfChildren(); i++) {
     Expression denominator = childAtIndex(i)->denominator(context, angleUnit);
-    if (denominator.isDefined()) {
+    if (!denominator.isUninitialized()) {
       // Make commonDenominator = LeastCommonMultiple(commonDenominator, denominator);
       commonDenominator.addMissingFactors(denominator, context, angleUnit);
     }
diff --git a/poincare/src/complex.cpp b/poincare/src/complex.cpp
index 0c3ff2b7b..1bee2f4d2 100644
--- a/poincare/src/complex.cpp
+++ b/poincare/src/complex.cpp
@@ -72,9 +72,9 @@ Expression ComplexNode<T>::complexToExpression(Preferences::ComplexFormat comple
           imag = Multiplication(Number::DecimalNumber(-this->imag()), Symbol(Ion::Charset::IComplex));
         }
       }
-      if (!imag.isDefined()) {
+      if (imag.isUninitialized()) {
         return real;
-      } else if (!real.isDefined()) {
+      } else if (real.isUninitialized()) {
         if (this->imag() > 0) {
           return imag;
         } else {
@@ -110,9 +110,9 @@ Expression ComplexNode<T>::complexToExpression(Preferences::ComplexFormat comple
         }
         exp = Power(Symbol(Ion::Charset::Exponential), arg);
       }
-      if (!exp.isDefined()) {
+      if (exp.isUninitialized()) {
         return norm;
-      } else if (!norm.isDefined()) {
+      } else if (norm.isUninitialized()) {
         return exp;
       } else {
         return Multiplication(norm, exp);
diff --git a/poincare/src/expression.cpp b/poincare/src/expression.cpp
index 8db9e7f95..abd0beb21 100644
--- a/poincare/src/expression.cpp
+++ b/poincare/src/expression.cpp
@@ -201,11 +201,13 @@ bool Expression::isEqualToItsApproximationLayout(Expression approximation, int b
 
 Expression Expression::ParseAndSimplify(const char * text, Context & context, Preferences::AngleUnit angleUnit) {
   Expression exp = parse(text);
-  if (!exp.isDefined()) {
+  if (exp.isUninitialized()) {
     return Undefined();
   }
   Expression reduced = exp.simplify(context, angleUnit);
-  if (!reduced.isDefined()) {
+  /* simplify might have been interrupted, in which case the resulting
+   * expression is uninitialized, so we need to check that. */
+  if (reduced.isUninitialized()) {
     return exp;
   }
   return reduced;
@@ -250,11 +252,8 @@ Expression Expression::deepBeautify(Context & context, Preferences::AngleUnit an
 
 template<typename U>
 Expression Expression::approximate(Context& context, Preferences::AngleUnit angleUnit, Preferences::Preferences::ComplexFormat complexFormat) const {
-  if (isDefined()) {
-    Evaluation<U> e = node()->approximate(U(), context, angleUnit);
-    return e.complexToExpression(complexFormat);
-  }
-  return Undefined();
+  Evaluation<U> e = node()->approximate(U(), context, angleUnit);
+  return e.complexToExpression(complexFormat);
 }
 
 template<typename U>
@@ -487,17 +486,17 @@ double Expression::nextIntersectionWithExpression(char symbol, double start, dou
   double extremumMax = std::isnan(result) ? max : result;
   Coordinate2D resultExtremum[2] = {
     nextMinimumOfExpression(symbol, start, step, extremumMax, [](char symbol, double x, Context & context, Preferences::AngleUnit angleUnit, const Expression expression0, const Expression expression1) {
-        if (expression1.isDefined()) {
-          return expression0.approximateWithValueForSymbol(symbol, x, context, angleUnit)-expression1.approximateWithValueForSymbol(symbol, x, context, angleUnit);
-        } else {
+        if (expression1.isUninitialized()) {
           return expression0.approximateWithValueForSymbol(symbol, x, context, angleUnit);
+        } else {
+          return expression0.approximateWithValueForSymbol(symbol, x, context, angleUnit)-expression1.approximateWithValueForSymbol(symbol, x, context, angleUnit);
         }
       }, context, angleUnit, expression, true),
     nextMinimumOfExpression(symbol, start, step, extremumMax, [](char symbol, double x, Context & context, Preferences::AngleUnit angleUnit, const Expression expression0, const Expression expression1) {
-        if (expression1.isDefined()) {
-          return expression1.approximateWithValueForSymbol(symbol, x, context, angleUnit)-expression0.approximateWithValueForSymbol(symbol, x, context, angleUnit);
-        } else {
+        if (expression1.isUninitialized()) {
           return -expression0.approximateWithValueForSymbol(symbol, x, context, angleUnit);
+        } else {
+          return expression1.approximateWithValueForSymbol(symbol, x, context, angleUnit)-expression0.approximateWithValueForSymbol(symbol, x, context, angleUnit);
         }
       }, context, angleUnit, expression, true)};
   for (int i = 0; i < 2; i++) {
diff --git a/poincare/src/global_context.cpp b/poincare/src/global_context.cpp
index 9ce4707b4..75a1bde34 100644
--- a/poincare/src/global_context.cpp
+++ b/poincare/src/global_context.cpp
@@ -43,7 +43,7 @@ const Expression GlobalContext::expressionForSymbol(const Symbol symbol) {
   if (index < 0 || index >= k_maxNumberOfScalarExpressions) {
     return Expression();
   }
-  if (m_expressions[index].isDefined()) {
+  if (!m_expressions[index].isUninitialized()) {
     return m_expressions[index];
   }
   return defaultExpression();
@@ -52,7 +52,7 @@ const Expression GlobalContext::expressionForSymbol(const Symbol symbol) {
 LayoutRef GlobalContext::layoutForSymbol(const Symbol symbol, int numberOfSignificantDigits) {
   if (Symbol::isMatrixSymbol(symbol.name())) {
     int index = symbolIndex(symbol);
-    if (!m_matrixLayouts[index].isDefined()) {
+    if (m_matrixLayouts[index].isUninitialized()) {
       m_matrixLayouts[index] = m_matrixExpressions[index].createLayout(Preferences::PrintFloatMode::Decimal, numberOfSignificantDigits);
     }
     return m_matrixLayouts[index];
@@ -65,8 +65,8 @@ void GlobalContext::setExpressionForSymbolName(const Expression expression, cons
  if (Symbol::isMatrixSymbol(symbol.name())) {
     int indexMatrix = symbol.name() - (char)Symbol::SpecialSymbols::M0;
     assert(indexMatrix >= 0 && indexMatrix < k_maxNumberOfMatrixExpressions);
-    Expression evaluation = expression.isDefined() ? expression.approximate<double>(context, Preferences::sharedPreferences()->angleUnit(), Preferences::sharedPreferences()->complexFormat()) : Expression(); // evaluate before deleting anything (to be able to evaluate M1+2->M1)
-    if (evaluation.isDefined()) {
+    Expression evaluation = expression.isUninitialized() ? Expression() : expression.approximate<double>(context, Preferences::sharedPreferences()->angleUnit(), Preferences::sharedPreferences()->complexFormat()); // evaluate before deleting anything (to be able to evaluate M1+2->M1)
+    if (!evaluation.isUninitialized()) {
       if (evaluation.type() != ExpressionNode::Type::Matrix) {
         m_matrixExpressions[indexMatrix] = Matrix(evaluation);
       } else {
@@ -78,8 +78,8 @@ void GlobalContext::setExpressionForSymbolName(const Expression expression, cons
   if (index < 0 || index >= k_maxNumberOfScalarExpressions) {
     return;
   }
-  Expression evaluation = expression.isDefined() ? expression.approximate<double>(context, Preferences::sharedPreferences()->angleUnit(), Preferences::sharedPreferences()->complexFormat()) : Expression(); // evaluate before deleting anything (to be able to evaluate A+2->A)
-  if (!evaluation.isDefined()) {
+  Expression evaluation = expression.isUninitialized() ? Expression() : expression.approximate<double>(context, Preferences::sharedPreferences()->angleUnit(), Preferences::sharedPreferences()->complexFormat()); // evaluate before deleting anything (to be able to evaluate A+2->A)
+  if (evaluation.isUninitialized()) {
     return;
   }
   if (evaluation.type() == ExpressionNode::Type::Matrix) {
diff --git a/poincare/src/layout_cursor.cpp b/poincare/src/layout_cursor.cpp
index 43c614514..9bddce8e7 100644
--- a/poincare/src/layout_cursor.cpp
+++ b/poincare/src/layout_cursor.cpp
@@ -173,7 +173,7 @@ void LayoutCursor::insertText(const char * text) {
       newChild = CharLayoutRef(Ion::Charset::MiddleDot);
     } else if (text[i] == '(') {
       newChild = CharLayoutRef('('); //TODO
-      if (!pointedChild.isDefined()) {
+      if (pointedChild.isUninitialized()) {
         pointedChild = newChild;
       }
     } else if (text[i] == ')') {
@@ -205,7 +205,7 @@ void LayoutCursor::insertText(const char * text) {
     }
     m_layoutRef.addSibling(this, newChild, true);
   }
-  if (pointedChild.isDefined() && pointedChild.parent().isDefined()) {
+  if (!pointedChild.isUninitialized() && !pointedChild.parent().isUninitialized()) {
     m_layoutRef = pointedChild;
   }
 }
@@ -276,7 +276,7 @@ bool LayoutCursor::baseForNewPowerLayout() {
       return true;
     }
     LayoutCursor equivalentLayoutCursor = m_layoutRef.equivalentCursor(this);
-    if (!equivalentLayoutCursor.layoutReference().isDefined()
+    if (equivalentLayoutCursor.layoutReference().isUninitialized()
         || (equivalentLayoutCursor.layoutReference().isHorizontal()
           && equivalentLayoutCursor.position() == Position::Left))
     {
@@ -300,12 +300,12 @@ bool LayoutCursor::privateShowHideEmptyLayoutIfNeeded(bool show) {
   } else {
     // Check the equivalent cursor position
     LayoutRef equivalentPointedLayout = m_layoutRef.equivalentCursor(this).layoutReference();
-    if (equivalentPointedLayout.isDefined() && equivalentPointedLayout.isEmpty()) {
+    if (!equivalentPointedLayout.isUninitialized() && equivalentPointedLayout.isEmpty()) {
       adjacentEmptyLayout = equivalentPointedLayout;
     }
   }
 
-  if (!adjacentEmptyLayout.isDefined()) {
+  if (adjacentEmptyLayout.isUninitialized()) {
     return false;
   }
   /* Change the visibility of the neighbouring empty layout: it might be either
diff --git a/poincare/src/layout_helper.cpp b/poincare/src/layout_helper.cpp
index 55d1437d4..6fbf9b057 100644
--- a/poincare/src/layout_helper.cpp
+++ b/poincare/src/layout_helper.cpp
@@ -46,7 +46,7 @@ LayoutRef LayoutHelper::Prefix(const Expression expression, Preferences::PrintFl
 LayoutRef LayoutHelper::Parentheses(LayoutRef layoutRef, bool cloneLayout) {
   HorizontalLayoutRef result;
   result.addChildAtIndex(LeftParenthesisLayoutRef(), 0, 0, nullptr);
-  if (layoutRef.isDefined()) {
+  if (!layoutRef.isUninitialized()) {
     result.addOrMergeChildAtIndex(cloneLayout ? layoutRef.clone() : layoutRef, 1, true);
   }
   result.addChildAtIndex(RightParenthesisLayoutRef(), result.numberOfChildren(), result.numberOfChildren(), nullptr);
diff --git a/poincare/src/layout_node.cpp b/poincare/src/layout_node.cpp
index 8c204a54b..0b1b0c6d9 100644
--- a/poincare/src/layout_node.cpp
+++ b/poincare/src/layout_node.cpp
@@ -237,7 +237,7 @@ void LayoutNode::scoreCursorInDescendantsVertically (
 bool LayoutNode::changeGreySquaresOfAllMatrixAncestors(bool add) {
   bool changedSquares = false;
   LayoutRef currentAncestor = LayoutRef(parent());
-  while (currentAncestor.isDefined()) {
+  while (!currentAncestor.isUninitialized()) {
     if (currentAncestor.isMatrix()) {
       if (add) {
         MatrixLayoutRef(static_cast<MatrixLayoutNode *>(currentAncestor.node())).addGreySquares();
diff --git a/poincare/src/layout_reference.cpp b/poincare/src/layout_reference.cpp
index b0685ec26..393853cfe 100644
--- a/poincare/src/layout_reference.cpp
+++ b/poincare/src/layout_reference.cpp
@@ -50,7 +50,7 @@ void LayoutReference::replaceWithJuxtapositionOf(LayoutRef leftChild, LayoutRef
     return;
   }
   LayoutReference p = parent();
-  assert(p.isDefined());
+  assert(!p.isUninitialized());
   if (!p.isHorizontal()) {
     /* One of the children to juxtapose might be "this", so we cannot just call
      * replaceWith. */
@@ -130,7 +130,7 @@ void LayoutReference::addSibling(LayoutCursor * cursor, LayoutReference sibling,
    * root layout. */
   LayoutRef rootLayout = root();
   LayoutRef p = parent();
-  assert(p.isDefined());
+  assert(!p.isUninitialized());
   if (p.isHorizontal()) {
     int indexInParent = p.indexOfChild(*this);
     int siblingIndex = cursor->position() == LayoutCursor::Position::Left ? indexInParent : indexInParent + 1;
@@ -145,7 +145,7 @@ void LayoutReference::addSibling(LayoutCursor * cursor, LayoutReference sibling,
       } else if (cursor->position() == LayoutCursor::Position::Right && indexInParent < p.numberOfChildren() - 1) {
         neighbour = p.childAtIndex(indexInParent + 1);
       }
-      if (neighbour.isDefined() && neighbour.isVerticalOffset()) {
+      if (!neighbour.isUninitialized() && neighbour.isVerticalOffset()) {
         if (moveCursor) {
           cursor->setLayoutReference(neighbour);
           cursor->setPosition(cursor->position() == LayoutCursor::Position::Left ? LayoutCursor::Position::Right : LayoutCursor::Position::Left);
@@ -198,7 +198,7 @@ void LayoutReference::removeChild(LayoutRef l, LayoutCursor * cursor, bool force
 
 void LayoutReference::collapseOnDirection(HorizontalDirection direction, int absorbingChildIndex) {
   LayoutRef p = parent();
-  if (!p.isDefined() || !p.isHorizontal()) {
+  if (p.isUninitialized() || !p.isHorizontal()) {
     return;
   }
   int idxInParent = p.indexOfChild(*this);
@@ -206,7 +206,7 @@ void LayoutReference::collapseOnDirection(HorizontalDirection direction, int abs
   int numberOfOpenParenthesis = 0;
   bool canCollapse = true;
   LayoutRef absorbingChild = childAtIndex(absorbingChildIndex);
-  if (!absorbingChild.isDefined() || !absorbingChild.isHorizontal()) {
+  if (absorbingChild.isUninitialized() || !absorbingChild.isHorizontal()) {
     return;
   }
   HorizontalLayoutRef horizontalAbsorbingChild = HorizontalLayoutRef(static_cast<HorizontalLayoutNode *>(absorbingChild.node()));
diff --git a/poincare/src/matrix.cpp b/poincare/src/matrix.cpp
index 6210f8535..7b01d6baa 100644
--- a/poincare/src/matrix.cpp
+++ b/poincare/src/matrix.cpp
@@ -183,7 +183,7 @@ Matrix Matrix::rowCanonize(Context & context, Preferences::AngleUnit angleUnit,
       // No non-null coefficient in this column, skip
       k++;
       // Update determinant: det *= 0
-      if (determinant.isDefined()) { determinant.addChildAtIndexInPlace(Rational(0), 0, determinant.numberOfChildren()); }
+      if (!determinant.isUninitialized()) { determinant.addChildAtIndexInPlace(Rational(0), 0, determinant.numberOfChildren()); }
     } else {
       // Swap row h and iPivot
       if (iPivot != h) {
@@ -191,12 +191,12 @@ Matrix Matrix::rowCanonize(Context & context, Preferences::AngleUnit angleUnit,
           matrix.swapChildrenInPlace(iPivot*n+col, h*n+col);
         }
         // Update determinant: det *= -1
-        if (determinant.isDefined()) { determinant.addChildAtIndexInPlace(Rational(-1), 0, determinant.numberOfChildren()); }
+        if (!determinant.isUninitialized()) { determinant.addChildAtIndexInPlace(Rational(-1), 0, determinant.numberOfChildren()); }
       }
       /* Set to 1 M[h][k] by linear combination */
       Expression divisor = matrixChild(h, k);
       // Update determinant: det *= divisor
-      if (determinant.isDefined()) { determinant.addChildAtIndexInPlace(divisor, 0, determinant.numberOfChildren()); }
+      if (!determinant.isUninitialized()) { determinant.addChildAtIndexInPlace(divisor, 0, determinant.numberOfChildren()); }
       for (int j = k+1; j < n; j++) {
         Expression opHJ = matrixChild(h, j);
         Expression newOpHJ = Division(opHJ, divisor);
diff --git a/poincare/src/power.cpp b/poincare/src/power.cpp
index e91083185..585d0affe 100644
--- a/poincare/src/power.cpp
+++ b/poincare/src/power.cpp
@@ -517,7 +517,7 @@ template<typename T> MatrixComplex<T> PowerNode::computeOnMatrixAndComplex(const
   }
   if (power < 0) {
     MatrixComplex<T> inverse = m.inverse();
-    if (!inverse.isDefined()) {
+    if (inverse.isUninitialized()) {
       return MatrixComplex<T>::Undefined();
     }
     Complex<T> minusC = Complex<T>(-d);
diff --git a/poincare/src/symbol.cpp b/poincare/src/symbol.cpp
index 811411d12..64dbc1a3a 100644
--- a/poincare/src/symbol.cpp
+++ b/poincare/src/symbol.cpp
@@ -156,10 +156,10 @@ Evaluation<T> SymbolNode::templatedApproximate(Context& context, Preferences::An
     return Complex<T>(0.0, 1.0);
   }
   const Expression e = context.expressionForSymbol(Symbol(m_name));
-  if (e.isDefined()) {
-    return e.node()->approximate(T(), context, angleUnit);
+  if (e.isUninitialized()) {
+    return Complex<T>::Undefined();
   }
-  return Complex<T>::Undefined();
+  return e.node()->approximate(T(), context, angleUnit);
 }
 
 const char * Symbol::textForSpecialSymbols(char name) {
@@ -302,12 +302,12 @@ Expression Symbol::shallowReduce(Context& context, Preferences::AngleUnit angleU
 #if 0
   // Do not replace symbols in expression of type: 3->A
   Expression p = parent();
-  if (p.isDefined() && p.type() == ExpressionNode::Type::Store && p.childAtIndex(1) == *this) {
+  if (!p.isUninitialized() && p.type() == ExpressionNode::Type::Store && p.childAtIndex(1) == *this) {
     return *this;
   }
 #endif
   const Expression e = context.expressionForSymbol(*this);
-  if (e.isDefined() && node()->hasAnExactRepresentation(context)) {
+  if (!e.isUninitialized() && node()->hasAnExactRepresentation(context)) {
     // TODO: later AZ should be replaced.
     /* The stored expression had been beautified which forces to call deepReduce. */
     return e.deepReduce(context, angleUnit);
@@ -319,7 +319,7 @@ Expression Symbol::replaceSymbolWithExpression(char symbol, Expression expressio
   if (name() == symbol) {
     Expression value = expression;
     Expression p = parent();
-    if (p.isDefined() && value.node()->needsParenthesesWithParent(p.node())) {
+    if (!p.isUninitialized() && value.node()->needsParenthesesWithParent(p.node())) {
       value = Parenthesis(value);
     }
     return value;
diff --git a/poincare/src/tree_by_reference.cpp b/poincare/src/tree_by_reference.cpp
index ef72ee470..d329f642f 100644
--- a/poincare/src/tree_by_reference.cpp
+++ b/poincare/src/tree_by_reference.cpp
@@ -9,16 +9,14 @@ namespace Poincare {
 /* Constructors */
 
 TreeByReference::~TreeByReference() {
-  if (isDefined()) {
-    assert(node()->identifier() == m_identifier);
-    node()->release(numberOfChildren()); //TODO No malformed nodes ?
-  }
+  assert(node()->identifier() == m_identifier);
+  node()->release(numberOfChildren()); //TODO No malformed nodes ?
 }
 
 /* Clone */
 
 TreeByReference TreeByReference::clone() const {
-  if (!isDefined()){
+  if (isUninitialized()){
     return TreeByReference();
   }
   TreeNode * myNode = node();
@@ -33,12 +31,12 @@ TreeByReference TreeByReference::clone() const {
 /* Hierarchy operations */
 
 void TreeByReference::replaceWithInPlace(TreeByReference t) {
-  assert(isDefined());
+  assert(!isUninitialized());
   if (isAllocationFailure()) {
     return;
   }
   TreeByReference p = parent();
-  if (p.isDefined()) {
+  if (!p.isUninitialized()) {
     p.replaceChildInPlace(*this, t);
   }
 }
@@ -48,7 +46,7 @@ void TreeByReference::replaceChildInPlace(TreeByReference oldChild, TreeByRefere
     return;
   }
 
-  assert(isDefined());
+  assert(!isUninitialized());
   if (isAllocationFailure()) {
     return;
   }
@@ -58,7 +56,7 @@ void TreeByReference::replaceChildInPlace(TreeByReference oldChild, TreeByRefere
   }
 
   // Move the new child
-  assert(!newChild.parent().isDefined());
+  assert(newChild.parent().isUninitialized());
   TreePool::sharedPool()->move(oldChild.node(), newChild.node(), newChild.numberOfChildren());
   /* We could have moved the new node to oldChild.node()->nextSibling(), but
    * nextSibling is not computed correctly if we inserted an
@@ -74,9 +72,9 @@ void TreeByReference::replaceWithAllocationFailureInPlace(int currentNumberOfChi
   if (isAllocationFailure()) {
     return;
   }
-  assert(isDefined());
+  assert(!isUninitialized());
   TreeByReference p = parent();
-  bool hasParent = p.isDefined();
+  bool hasParent = !p.isUninitialized();
   int indexInParentNode = hasParent ? node()->indexInParent() : -1;
   int currentRetainCount = node()->retainCount();
   TreeNode * staticAllocFailNode = node()->failedAllocationStaticNode();
@@ -100,7 +98,7 @@ void TreeByReference::replaceWithAllocationFailureInPlace(int currentNumberOfChi
   TreeNode * newAllocationFailureNode = TreePool::sharedPool()->deepCopy(staticAllocFailNode);
   newAllocationFailureNode->rename(m_identifier, true);
   newAllocationFailureNode->retain();
-  if (p.isDefined()) {
+  if (hasParent) {
     assert(indexInParentNode >= 0);
     /* Set the refCount to previousRefCount-1 because the previous parent is
      * no longer retaining the node. When we add this node to the parent, it
@@ -138,7 +136,7 @@ void TreeByReference::mergeChildrenAtIndexInPlace(TreeByReference t, int i) {
 }
 
 void TreeByReference::swapChildrenInPlace(int i, int j) {
-  assert(isDefined());
+  assert(!isStatic());
   assert(i >= 0 && i < numberOfChildren());
   assert(j >= 0 && j < numberOfChildren());
   if (i == j) {
@@ -163,7 +161,7 @@ void TreeByReference::log() const {
 
 // Add
 void TreeByReference::addChildAtIndexInPlace(TreeByReference t, int index, int currentNumberOfChildren) {
-  assert(isDefined());
+  assert(!isUninitialized());
   if (node()->isAllocationFailure()) {
     return;
   }
@@ -173,7 +171,7 @@ void TreeByReference::addChildAtIndexInPlace(TreeByReference t, int index, int c
   }
   assert(index >= 0 && index <= currentNumberOfChildren);
 
-  assert(!t.parent().isDefined());
+  assert(t.parent().isUninitialized());
   // Move t
   TreeNode * newChildPosition = node()->next();
   for (int i = 0; i < index; i++) {
@@ -189,21 +187,21 @@ void TreeByReference::addChildAtIndexInPlace(TreeByReference t, int index, int c
 // Remove
 
 void TreeByReference::removeChildAtIndexInPlace(int i) {
-  assert(isDefined());
+  assert(!isUninitialized());
   assert(i >= 0 && i < numberOfChildren());
   TreeByReference t = childAtIndex(i);
   removeChildInPlace(t, t.numberOfChildren());
 }
 
 void TreeByReference::removeChildInPlace(TreeByReference t, int childNumberOfChildren) {
-  assert(isDefined());
+  assert(!isUninitialized());
   TreePool::sharedPool()->move(TreePool::sharedPool()->last(), t.node(), childNumberOfChildren);
   t.node()->release(childNumberOfChildren);
   node()->decrementNumberOfChildren();
 }
 
 void TreeByReference::removeChildrenInPlace(int currentNumberOfChildren) {
-  assert(isDefined());
+  assert(!isUninitialized());
   for (int i = 0; i < currentNumberOfChildren; i++) {
     TreeByReference childRef = childAtIndex(0);
     TreePool::sharedPool()->move(TreePool::sharedPool()->last(), childRef.node(), childRef.numberOfChildren());
diff --git a/poincare/src/variable_context.cpp b/poincare/src/variable_context.cpp
index f3f202d8f..e128bed15 100644
--- a/poincare/src/variable_context.cpp
+++ b/poincare/src/variable_context.cpp
@@ -22,7 +22,7 @@ void VariableContext<T>::setApproximationForVariable(T value) {
 template<typename T>
 void VariableContext<T>::setExpressionForSymbolName(const Expression expression, const Symbol symbol, Context & context) {
   if (symbol.name() == m_name) {
-    if (!expression.isDefined()) {
+    if (expression.isUninitialized()) {
       return;
     }
     m_value = Float<T>(expression.approximateToScalar<T>(context, Preferences::sharedPreferences()->angleUnit()));
diff --git a/poincare/src/vertical_offset_layout_node.cpp b/poincare/src/vertical_offset_layout_node.cpp
index 85d43bae2..5d2e9cb08 100644
--- a/poincare/src/vertical_offset_layout_node.cpp
+++ b/poincare/src/vertical_offset_layout_node.cpp
@@ -271,7 +271,7 @@ bool VerticalOffsetLayoutNode::willAddSibling(LayoutCursor * cursor, LayoutNode
         assert(cursor->position() == LayoutCursor::Position::Left);
         parentRef.addChildAtIndex(rightParenthesis, idxInParent, parentRef.numberOfChildren(), nullptr);
       }
-      if (rightParenthesis.parent().isDefined()) {
+      if (!rightParenthesis.parent().isUninitialized()) {
         cursor->setLayoutReference(rightParenthesis);
       }
       if (rootLayout.isAllocationFailure()) {
diff --git a/poincare/test/helper.cpp b/poincare/test/helper.cpp
index 1f0cbf92a..e8c949add 100644
--- a/poincare/test/helper.cpp
+++ b/poincare/test/helper.cpp
@@ -49,7 +49,7 @@ Expression parse_expression(const char * expression) {
   strlcpy(buffer, expression, sizeof(buffer));
   translate_in_special_chars(buffer);
   Expression result = Expression::parse(buffer);
-  assert(result.isDefined());
+  assert(!result.isUninitialized());
   return result;
 }