diff --git a/apps/regression/regression_context.cpp b/apps/regression/regression_context.cpp
index 4e28c0769..da8443c20 100644
--- a/apps/regression/regression_context.cpp
+++ b/apps/regression/regression_context.cpp
@@ -9,8 +9,8 @@ using namespace Shared;
 
 namespace Regression {
 
-const Expression RegressionContext::expressionForSymbol(const Symbol & symbol) {
-  if (Symbol::isRegressionSymbol(symbol.name())) {
+const Expression RegressionContext::expressionForSymbol(const SymbolAbstract & symbol) {
+  if (symbol.type() == ExpressionNode::Type::Symbol && Symbol::isRegressionSymbol(symbol.name())) {
     const char * seriesName = symbol.name();
     assert(strlen(seriesName) == 2);
 
@@ -23,9 +23,9 @@ const Expression RegressionContext::expressionForSymbol(const Symbol & symbol) {
     assert(m_seriesPairIndex >= 0);
     assert(m_seriesPairIndex < m_store->numberOfPairsOfSeries(series));
     return Float<double>(m_store->get(series, storeI, m_seriesPairIndex));
-  } else {
-    return m_parentContext->expressionForSymbol(symbol);
   }
+} else {
+  return m_parentContext->expressionForSymbol(symbol);
 }
 
 }
diff --git a/apps/sequence/cache_context.cpp b/apps/sequence/cache_context.cpp
index 1e284a751..878e6d82b 100644
--- a/apps/sequence/cache_context.cpp
+++ b/apps/sequence/cache_context.cpp
@@ -15,10 +15,12 @@ CacheContext<T>::CacheContext(Context * parentContext) :
 }
 
 template<typename T>
-const Expression CacheContext<T>::expressionForSymbol(const Symbol & symbol) {
+const Expression CacheContext<T>::expressionForSymbol(const SymbolAbstract & symbol) {
   // [u|v](n(+1)?)
-  if ((symbol.name()[0] ==  SequenceStore::k_sequenceNames[0][0] || symbol.name()[0] ==  SequenceStore::k_sequenceNames[1][0])
-   && (strcmp(symbol.name()+1, "(n)") == 0 || strcmp(symbol.name()+1, "(n+1)") == 0)) {
+  if (symbol.type() == ExpressionNode::Type::Symbol
+    && (symbol.name()[0] ==  SequenceStore::k_sequenceNames[0][0] || symbol.name()[0] ==  SequenceStore::k_sequenceNames[1][0])
+    && (strcmp(symbol.name()+1, "(n)") == 0 || strcmp(symbol.name()+1, "(n+1)") == 0))
+  {
     return Float<T>(m_values[nameIndexForSymbol(symbol)][rankIndexForSymbol(symbol)]);
   }
   return VariableContext::expressionForSymbol(symbol);
diff --git a/apps/statistics/statistics_context.cpp b/apps/statistics/statistics_context.cpp
index 88f351610..46f744c00 100644
--- a/apps/statistics/statistics_context.cpp
+++ b/apps/statistics/statistics_context.cpp
@@ -9,8 +9,8 @@ using namespace Shared;
 
 namespace Statistics {
 
-const Expression StatisticsContext::expressionForSymbol(const Symbol & symbol) {
-  if (Symbol::isSeriesSymbol(symbol.name())) {
+const Expression StatisticsContext::expressionForSymbol(const SymbolAbstract & symbol) {
+  if (symbol.type() == ExpressionNode::Type::Symbol && Symbol::isSeriesSymbol(symbol.name())) {
     const char * seriesName = symbol.name();
     assert(strlen(seriesName) == 2);
 
diff --git a/poincare/Makefile b/poincare/Makefile
index 9c06e04c4..cea4501fe 100644
--- a/poincare/Makefile
+++ b/poincare/Makefile
@@ -120,6 +120,7 @@ objs += $(addprefix poincare/src/,\
   subtraction.o\
   sum.o\
   symbol.o\
+  symbol_abstract.o\
   tangent.o\
   tree_handle.o\
   tree_node.o\
diff --git a/poincare/include/poincare/context.h b/poincare/include/poincare/context.h
index c53b34de9..41cb9a0ad 100644
--- a/poincare/include/poincare/context.h
+++ b/poincare/include/poincare/context.h
@@ -4,11 +4,12 @@
 namespace Poincare {
 
 class Expression;
-class Symbol;
+class SymbolAbstract;
+class Symbol; //TODO remove?
 
 class Context {
 public:
-  virtual const Expression expressionForSymbol(const Symbol & symbol) = 0;
+  virtual const Expression expressionForSymbol(const SymbolAbstract & symbol) = 0;
   virtual void setExpressionForSymbol(const Expression & expression, const Symbol & symbol, Context & context) = 0;
 };
 
diff --git a/poincare/include/poincare/function.h b/poincare/include/poincare/function.h
index 06c5e30ed..47d51e848 100644
--- a/poincare/include/poincare/function.h
+++ b/poincare/include/poincare/function.h
@@ -1,14 +1,18 @@
 #ifndef POINCARE_FUNCTION_H
 #define POINCARE_FUNCTION_H
 
-#include <poincare/symbol.h>
+#include <poincare/symbol_abstract.h>
 #include <poincare/variable_context.h>
 
 namespace Poincare {
 
-class FunctionNode : public SymbolNode  {
+class FunctionNode : public SymbolAbstractNode  {
 public:
+  // SymbolAbstractNode
+  const char * name() const override { return m_name; }
+
   // TreeNode
+  void initToMatchSize(size_t goalSize) override;
   size_t size() const override;
   int numberOfChildren() const override { return 1; } //TODO allow any number of children? Needs templating
 #if POINCARE_TREE_LOG
@@ -19,6 +23,7 @@ public:
 
   // Properties
   Type type() const override { return Type::Function; }
+  Sign sign() const override { return Sign::Unknown; }
   Expression replaceSymbolWithExpression(const Symbol & symbol, const Expression & expression) override;
   int polynomialDegree(Context & context, const char * symbolName) const override;
   int getPolynomialCoefficients(Context & context, const char * symbolName, Expression coefficients[]) const override;
@@ -26,6 +31,8 @@ public:
   float characteristicXRange(Context & context, Preferences::AngleUnit angleUnit) const override;
 
 private:
+  char m_name[0]; // MUST be the last member variable
+
   VariableContext xContext(Context & parentContext) const;
   // Layout
   Layout createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
@@ -37,10 +44,10 @@ private:
   Evaluation<double> approximate(DoublePrecision p, Context& context, Preferences::AngleUnit angleUnit) const override;
 };
 
-class Function : public Symbol {
+class Function : public SymbolAbstract {
 public:
   explicit Function(const char * name);
-  Function(const FunctionNode * n) : Symbol(n) {}
+  Function(const FunctionNode * n) : SymbolAbstract(n) {}
   explicit Function(const char * name, Expression operand) : Function(name) {
     replaceChildAtIndexInPlace(0, operand);
   }
diff --git a/poincare/include/poincare/global_context.h b/poincare/include/poincare/global_context.h
index b0840d12b..a0eefef1b 100644
--- a/poincare/include/poincare/global_context.h
+++ b/poincare/include/poincare/global_context.h
@@ -19,7 +19,7 @@ public:
   static constexpr char expExtension[] = "exp";
   /* The expression recorded in global context is already a expression.
    * Otherwise, we would need the context and the angle unit to evaluate it */
-  const Expression expressionForSymbol(const Symbol & symbol) override;
+  const Expression expressionForSymbol(const SymbolAbstract & symbol) override;
   void setExpressionForSymbol(const Expression & expression, const Symbol & symbol, Context & context) override;
   static Ion::Storage::Record RecordWithName(const char * name);
   static bool storageMemoryFull();
diff --git a/poincare/include/poincare/symbol.h b/poincare/include/poincare/symbol.h
index 0c55fbd8e..201609acb 100644
--- a/poincare/include/poincare/symbol.h
+++ b/poincare/include/poincare/symbol.h
@@ -1,30 +1,16 @@
 #ifndef POINCARE_SYMBOL_H
 #define POINCARE_SYMBOL_H
 
-#include <poincare/expression.h>
+#include <poincare/symbol_abstract.h>
 
 namespace Poincare {
 
-/* TODO: should we keep the size of SymbolNode as a member to speed up TreePool
- * scan? */
-
-/* Symbol Node contains an empty member variable "m_name", which is used to get
- * the string that follows. This means that a SymbolNode's size is sizeo
- * (SymbolNode) + strlen(string).
- *
- *   Seen by TreePool:    |SymbolNode                               |
- *   SymbolNode layout:   |ExpressionNode|m_name|                   |
- *   Memory content:      |ExpressionNode|S     |y|m|b|o|l|N|a|m|e|0|
- * */
-
-class SymbolNode final : public ExpressionNode {
-  friend class Store;
+class SymbolNode final : public SymbolAbstractNode {
 public:
-  void initToMatchSize(size_t goalSize) override;
-  void setName(const char * name, int length) { strlcpy(m_name, name, length+1); }
-  const char * name() const { return m_name; }
+  const char * name() const override { return m_name; }
 
   // TreeNode
+  void initToMatchSize(size_t goalSize) override;
   size_t size() const override;
   int numberOfChildren() const override { return 0; }
 #if POINCARE_TREE_LOG
@@ -45,10 +31,7 @@ public:
   int getVariables(Context & context, isVariableTest isVariable, char * variables, int maxSizeVariable) const override;
   float characteristicXRange(Context & context, Preferences::AngleUnit angleUnit) const override;
 
-  /* Comparison */
-  int simplificationOrderSameType(const ExpressionNode * e, bool canBeInterrupted) const override;
-
-/* Layout */
+  /* Layout */
   Layout createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
   int serialize(char * buffer, int bufferSize, Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const override;
 
@@ -64,14 +47,14 @@ public:
   bool isPi() const { return isSymbolChar(Ion::Charset::SmallPi); }
   bool isExponential() const { return isSymbolChar(Ion::Charset::Exponential); }
   bool isIComplex() const { return isSymbolChar(Ion::Charset::IComplex); }
-protected:
-  char m_name[0]; // MUST be the last member variable
 private:
+  char m_name[0]; // MUST be the last member variable
+
   template<typename T> Evaluation<T> templatedApproximate(Context& context, Preferences::AngleUnit angleUnit) const;
   bool isSymbolChar(char c) const { const char symbolName[2] = {c, 0}; return strcmp(m_name, symbolName) == 0; }
 };
 
-class Symbol final : public Expression {
+class Symbol final : public SymbolAbstract {
   friend class Expression;
   friend class Store;
 public:
@@ -83,7 +66,7 @@ public:
   };
   Symbol(const char * name, int length);
   Symbol(char name);
-  Symbol(const SymbolNode * node) : Expression(node) {}
+  Symbol(const SymbolNode * node) : SymbolAbstract(node) {}
 
   // Symbol properties
   bool isPi() const { return node()->isPi(); }
@@ -97,9 +80,6 @@ public:
   Expression shallowReduce(Context & context, Preferences::AngleUnit angleUnit, bool replaceSymbols = true);
   Expression replaceSymbolWithExpression(const Symbol & symbol, const Expression & expression);
   int getPolynomialCoefficients(Context & context, const char * symbolName, Expression coefficients[]) const;
-
-  // Symbol
-  const char * name() const { return node()->name(); }
 private:
   SymbolNode * node() const { return static_cast<SymbolNode *>(Expression::node()); }
 };
diff --git a/poincare/include/poincare/symbol_abstract.h b/poincare/include/poincare/symbol_abstract.h
new file mode 100644
index 000000000..32812f698
--- /dev/null
+++ b/poincare/include/poincare/symbol_abstract.h
@@ -0,0 +1,53 @@
+#ifndef POINCARE_ABSTRACT_SYMBOL_H
+#define POINCARE_ABSTRACT_SYMBOL_H
+
+#include <poincare/expression.h>
+
+namespace Poincare {
+
+/* TODO: should we keep the size of SymbolAbstractNode as a member to speed up
+ * TreePool scan? */
+
+/* SymbolAbstract derived classes must have a char[0] member variable as their
+ * last member variable, so they can access their name, which is the string that
+ * follows the node in memory.
+ * This means that a DerivedSymbolNode's size is sizeof(DerivedSymbolNode) +
+ * strlen(string).
+ *
+ * For instance:
+ *   Seen by TreePool:    |SymbolNode                               |
+ *   SymbolNode layout:   |ExpressionNode|m_name|                   |
+ *   Memory content:      |ExpressionNode|S     |y|m|b|o|l|N|a|m|e|0|
+ * */
+
+class SymbolAbstractNode : public ExpressionNode {
+  friend class Store;
+public:
+  virtual const char * name() const = 0;
+  void setName(const char * newName, int length);
+
+  // ExpressionNode
+  int simplificationOrderSameType(const ExpressionNode * e, bool canBeInterrupted) const override;
+
+  // TreeNode
+#if POINCARE_TREE_LOG
+  virtual void logNodeName(std::ostream & stream) const override {
+    stream << "SymbolAbstract";
+  }
+#endif
+
+protected:
+  void initName(size_t nameSize);
+};
+
+class SymbolAbstract : public Expression {
+public:
+  const char * name() const { return node()->name(); }
+protected:
+  SymbolAbstract(const SymbolAbstractNode * node) : Expression(node) {}
+  SymbolAbstractNode * node() const { return static_cast<SymbolAbstractNode *>(Expression::node()); }
+};
+
+}
+
+#endif
diff --git a/poincare/include/poincare/variable_context.h b/poincare/include/poincare/variable_context.h
index 435928ab7..d4d8da0aa 100644
--- a/poincare/include/poincare/variable_context.h
+++ b/poincare/include/poincare/variable_context.h
@@ -14,7 +14,7 @@ public:
 
   // Context
   void setExpressionForSymbol(const Expression & expression, const Symbol & symbol, Context & context) override;
-  const Expression expressionForSymbol(const Symbol & symbol) override;
+  const Expression expressionForSymbol(const SymbolAbstract & symbol) override;
 
 private:
   const char * m_name;
diff --git a/poincare/src/function.cpp b/poincare/src/function.cpp
index ef0c6fc35..e2984e2ff 100644
--- a/poincare/src/function.cpp
+++ b/poincare/src/function.cpp
@@ -5,6 +5,7 @@
 #include <poincare/rational.h>
 #include <poincare/serialization_helper.h>
 #include <poincare/simplification_helper.h>
+#include <poincare/symbol.h>
 #include <cmath>
 
 namespace Poincare {
@@ -15,6 +16,15 @@ static size_t NodeSize(size_t nameLength) {
   return Helpers::AlignedSize(sizeof(FunctionNode)+nameLength+1, 4);
 }
 
+void FunctionNode::initToMatchSize(size_t goalSize) {
+  // TODO Factorize with symbol
+  assert(goalSize != sizeof(FunctionNode));
+  assert(goalSize > sizeof(FunctionNode));
+  size_t nameSize = goalSize - sizeof(FunctionNode);
+  SymbolAbstractNode::initName(nameSize);
+  assert(size() == goalSize);
+}
+
 size_t FunctionNode::size() const {
   return NodeSize(strlen(m_name));
 }
@@ -109,7 +119,7 @@ Expression Function::replaceSymbolWithExpression(const Symbol & symbol, const Ex
   if (symbol.type() == ExpressionNode::Type::Function && strcmp(name(), symbol.name()) == 0) {
     Expression value = expression.clone();
     // Replace the unknown in the new expression by the function's child
-    const char x[2] = {SpecialSymbols::UnknownX, 0};
+    const char x[2] = {Symbol::SpecialSymbols::UnknownX, 0};
     Symbol xSymbol = Symbol(x, 1);
     Expression xValue = childAtIndex(0);
     value.replaceSymbolWithExpression(xSymbol, xValue);
diff --git a/poincare/src/global_context.cpp b/poincare/src/global_context.cpp
index 3f2940baf..8640562fe 100644
--- a/poincare/src/global_context.cpp
+++ b/poincare/src/global_context.cpp
@@ -22,13 +22,16 @@ bool GlobalContext::storageMemoryFull() {
 
 /**/
 
-const Expression GlobalContext::expressionForSymbol(const Symbol & symbol) {
-  // Constant symbols
-  if (symbol.isPi()) {
-    return Float<double>(M_PI);
-  }
-  if (symbol.isExponential()) {
-    return Float<double>(M_E);
+const Expression GlobalContext::expressionForSymbol(const SymbolAbstract & symbol) {
+  if (symbol.type() == ExpressionNode::Type::Symbol) {
+    // Constant symbols
+    Symbol s = static_cast<const Symbol &>(symbol);
+    if (s.isPi()) {
+      return Float<double>(M_PI);
+    }
+    if (s.isExponential()) {
+      return Float<double>(M_E);
+    }
   }
   // Look up the file system for symbol
   return Expression::ExpressionFromRecord(RecordWithName(symbol.name()));
diff --git a/poincare/src/symbol.cpp b/poincare/src/symbol.cpp
index ffb4f9224..fcee778f9 100644
--- a/poincare/src/symbol.cpp
+++ b/poincare/src/symbol.cpp
@@ -17,11 +17,9 @@ constexpr char Symbol::k_ans[];
 
 void SymbolNode::initToMatchSize(size_t goalSize) {
   assert(goalSize != sizeof(SymbolNode));
-  int nameSize = goalSize - sizeof(SymbolNode);
-  for (int i = 0; i < nameSize - 1; i++) {
-    m_name[i] = 'a';
-  }
-  m_name[nameSize-1] = 0;
+  assert(goalSize > sizeof(SymbolNode));
+  size_t nameSize = goalSize - sizeof(SymbolNode);
+  SymbolAbstractNode::initName(nameSize);
   assert(size() == goalSize);
 }
 
@@ -99,11 +97,6 @@ float SymbolNode::characteristicXRange(Context & context, Preferences::AngleUnit
   return 0.0;
 }
 
-int SymbolNode::simplificationOrderSameType(const ExpressionNode * e, bool canBeInterrupted) const {
-  assert(e->type() == Type::Symbol);
-  return strcmp(m_name, static_cast<const SymbolNode *>(e)->name());
-}
-
 Layout SymbolNode::createLayout(Preferences::PrintFloatMode floatDisplayMode, int numberOfSignificantDigits) const {
   if (m_name[0] == Symbol::SpecialSymbols::UnknownX) {
     assert(m_name[1] == 0);
@@ -172,7 +165,7 @@ Evaluation<T> SymbolNode::templatedApproximate(Context& context, Preferences::An
   return e.approximateToEvaluation<T>(context, angleUnit);
 }
 
-Symbol::Symbol(const char * name, int length) : Expression(TreePool::sharedPool()->createTreeNode<SymbolNode>(NodeSize(length))) {
+Symbol::Symbol(const char * name, int length) : SymbolAbstract(TreePool::sharedPool()->createTreeNode<SymbolNode>(NodeSize(length))) {
   node()->setName(name, length);
 }
 
diff --git a/poincare/src/symbol_abstract.cpp b/poincare/src/symbol_abstract.cpp
new file mode 100644
index 000000000..f809dc1a0
--- /dev/null
+++ b/poincare/src/symbol_abstract.cpp
@@ -0,0 +1,23 @@
+#include <poincare/symbol_abstract.h>
+#include <string.h>
+
+namespace Poincare {
+
+void SymbolAbstractNode::setName(const char * newName, int length) {
+  strlcpy(const_cast<char*>(name()), newName, length+1);
+}
+
+int SymbolAbstractNode::simplificationOrderSameType(const ExpressionNode * e, bool canBeInterrupted) const {
+  assert(e->type() == Type::Symbol || e->type() == Type::Function);
+  return strcmp(name(), static_cast<const SymbolAbstractNode *>(e)->name());
+}
+
+void SymbolAbstractNode::initName(size_t nameSize) {
+  char * modifiableName = const_cast<char *>(name());
+  for (int i = 0; i < nameSize - 1; i++) {
+    modifiableName[i] = 'a';
+  }
+  modifiableName[nameSize-1] = 0;
+}
+
+}
diff --git a/poincare/src/variable_context.cpp b/poincare/src/variable_context.cpp
index ab364d15d..65ca57eec 100644
--- a/poincare/src/variable_context.cpp
+++ b/poincare/src/variable_context.cpp
@@ -29,7 +29,7 @@ void VariableContext::setExpressionForSymbol(const Expression & expression, cons
   }
 }
 
-const Expression VariableContext::expressionForSymbol(const Symbol & symbol) {
+const Expression VariableContext::expressionForSymbol(const SymbolAbstract & symbol) {
   if (strcmp(symbol.name(), m_name) == 0) {
     return m_value;
   } else {