diff --git a/apps/shared/expression_model_handle.cpp b/apps/shared/expression_model_handle.cpp
index a0ccf79c9..2faf4339e 100644
--- a/apps/shared/expression_model_handle.cpp
+++ b/apps/shared/expression_model_handle.cpp
@@ -74,12 +74,16 @@ bool ExpressionModelHandle::isEmpty() {
   return value().size <= metaDataSize();
 }
 
-void ExpressionModelHandle::tidy() {
+void ExpressionModelHandle::tidyExpressionModel() {
   m_layout = Layout();
   m_expression = Expression();
   m_circular = 0;
 }
 
+void ExpressionModelHandle::tidy() {
+  tidyExpressionModel();
+}
+
 Ion::Storage::Record::ErrorStatus ExpressionModelHandle::setContent(const char * c) {
   Expression expressionToStore;
   // if c = "", we want to reinit the Expression
@@ -113,10 +117,8 @@ Ion::Storage::Record::ErrorStatus ExpressionModelHandle::setExpressionContent(Ex
   }
   /* We cannot call tidy here because tidy is a virtual function and does not
    * do the same thing for all children class. And here we want to delete only
-   * the m_layout and m_expression. */
-  m_layout = Layout();
-  m_expression = Expression();
-  m_circular = 0;
+   * the elements relative to the ExpressionModel. */
+  tidyExpressionModel();
   return error;
 }
 
diff --git a/apps/shared/expression_model_handle.h b/apps/shared/expression_model_handle.h
index 0edb27278..4a90f529d 100644
--- a/apps/shared/expression_model_handle.h
+++ b/apps/shared/expression_model_handle.h
@@ -26,7 +26,13 @@ public:
   virtual bool isDefined();
   virtual bool isEmpty();
   virtual bool shouldBeClearedBeforeRemove() { return !isEmpty(); }
+  /* tidy is responsible to tidy the whole model whereas tidyExpressionModel
+   * tidies only the members associated with the ExpressionModel. In
+   * ExpressionModelHandle, tidy and tidyExpressionModel trigger the same
+   * behaviour but it is not true for its child classes (for example, in
+   * Sequence). */
   virtual void tidy();
+  virtual void tidyExpressionModel();
   virtual Ion::Storage::Record::ErrorStatus setContent(const char * c);
   Ion::Storage::Record::ErrorStatus setExpressionContent(Poincare::Expression & e);
 protected:
diff --git a/apps/solver/equation.cpp b/apps/solver/equation.cpp
index fa10a8c09..af923c078 100644
--- a/apps/solver/equation.cpp
+++ b/apps/solver/equation.cpp
@@ -1,4 +1,5 @@
 #include "equation.h"
+#include <poincare/constant.h>
 #include <poincare/equal.h>
 #include <poincare/undefined.h>
 #include <poincare/unreal.h>
@@ -6,29 +7,27 @@
 #include <ion/unicode/utf8_helper.h>
 
 using namespace Poincare;
+using namespace Shared;
 
 namespace Solver {
 
-Equation::Equation() :
-  Shared::ExpressionModel(),
+constexpr char Equation::extension[];
+
+Equation::Equation(Ion::Storage::Record record) :
+  ExpressionModelHandle(record),
   m_standardForm()
 {
 }
 
-void Equation::setContent(const char * c) {
-  /* ExpressionModel::setContent takes care of tidying m_expression and m_layout. */
-  tidyStandardForm();
-  ExpressionModel::setContent(c);
-}
-
-void Equation::tidy() {
-  ExpressionModel::tidy();
-  tidyStandardForm();
+void Equation::tidyExpressionModel() {
+  ExpressionModelHandle::tidyExpressionModel();
+  // Free the pool of the m_standardForm
+  m_standardForm = Expression();
 }
 
 Expression Equation::standardForm(Context * context) const {
   if (m_standardForm.isUninitialized()) {
-    const Expression e = expression(context);
+    const Expression e = expressionReduced(context);
     if (e.type() == ExpressionNode::Type::Unreal) {
       m_standardForm = Unreal::Builder();
       return m_standardForm;
@@ -39,7 +38,7 @@ Expression Equation::standardForm(Context * context) const {
     }
     if (e.type() == ExpressionNode::Type::Equal) {
       Preferences * preferences = Preferences::sharedPreferences();
-      m_standardForm = static_cast<const Equal&>(e).standardEquation(*context, Expression::UpdatedComplexFormatWithTextInput(preferences->complexFormat(), text()), preferences->angleUnit());
+      m_standardForm = static_cast<const Equal&>(e).standardEquation(*context, Expression::UpdatedComplexFormatWithExpressionInput(preferences->complexFormat(), expressionClone(), *context), preferences->angleUnit());
     } else {
       assert(e.type() == ExpressionNode::Type::Rational && static_cast<const Rational&>(e).isOne());
       // The equality was reduced which means the equality was always true.
@@ -49,13 +48,8 @@ Expression Equation::standardForm(Context * context) const {
   return m_standardForm;
 }
 
-bool Equation::containsIComplex() const {
-  return *(UTF8Helper::CodePointSearch(text(), UCodePointMathematicalBoldSmallI)) != 0;
-}
-
-void Equation::tidyStandardForm() {
-  // Free the pool of the m_standardForm
-  m_standardForm = Expression();
+bool Equation::containsIComplex(Context * context) const {
+  return expressionClone().recursivelyMatches([](const Expression e, Context & context, bool replaceSymbols) { return e.type() == ExpressionNode::Type::Constant && static_cast<const Constant &>(e).isIComplex(); }, *context, true);
 }
 
 }
diff --git a/apps/solver/equation.h b/apps/solver/equation.h
index de5688753..222bb19b3 100644
--- a/apps/solver/equation.h
+++ b/apps/solver/equation.h
@@ -1,22 +1,23 @@
 #ifndef SOLVER_EQUATION_h
 #define SOLVER_EQUATION_h
 
-#include "../shared/expression_model.h"
+#include "../shared/expression_model_handle.h"
 
 namespace Solver {
 
-class Equation : public Shared::ExpressionModel {
+class Equation : public Shared::ExpressionModelHandle {
 public:
-  Equation();
-  void setContent(const char * c) override;
-  void tidy() override;
+  Equation(Ion::Storage::Record record = Record());
+  void tidyExpressionModel() override;
   bool shouldBeClearedBeforeRemove() override {
     return false;
   }
   Poincare::Expression standardForm(Poincare::Context * context) const;
-  bool containsIComplex() const;
+  bool containsIComplex(Poincare::Context * context) const;
+
+  static constexpr char extension[] = "eq"; // TODO: store this elsewhere?
 private:
-  void tidyStandardForm();
+  size_t metaDataSize() const override { return 0; }
   mutable Poincare::Expression m_standardForm;
 };