diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index 5eacbb45c..e6699ca1a 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -214,7 +214,7 @@ public:
   void simplifyAndApproximate(Expression * simplifiedExpression, Expression * approximateExpression, Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit, bool symbolicComputation = true);
   Expression reduce(Context * context, Preferences::ComplexFormat complexFormat, Preferences::AngleUnit angleUnit);
 
-  Expression mapOnMatrixChild(ExpressionNode::ReductionContext reductionContext);
+  Expression mapOnMatrixFirstChild(ExpressionNode::ReductionContext reductionContext);
   static Expression ExpressionWithoutSymbols(Expression expressionWithSymbols, Context * context);
   Expression radianToDegree();
   Expression degreeToRadian();
diff --git a/poincare/src/absolute_value.cpp b/poincare/src/absolute_value.cpp
index 8c3768ddf..037306c1a 100644
--- a/poincare/src/absolute_value.cpp
+++ b/poincare/src/absolute_value.cpp
@@ -37,7 +37,7 @@ Expression AbsoluteValue::shallowReduce(ExpressionNode::ReductionContext reducti
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.isReal(reductionContext.context())) {
     float app = c.node()->approximate(float(), reductionContext.context(), reductionContext.complexFormat(), reductionContext.angleUnit()).toScalar();
diff --git a/poincare/src/arc_cosine.cpp b/poincare/src/arc_cosine.cpp
index 6b90aaaad..9980d0bd5 100644
--- a/poincare/src/arc_cosine.cpp
+++ b/poincare/src/arc_cosine.cpp
@@ -57,7 +57,7 @@ Expression ArcCosine::shallowReduce(ExpressionNode::ReductionContext reductionCo
     }
   }
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   return Trigonometry::shallowReduceInverseFunction(*this, reductionContext);
 }
diff --git a/poincare/src/arc_sine.cpp b/poincare/src/arc_sine.cpp
index f6e893a79..f62eaa7c9 100644
--- a/poincare/src/arc_sine.cpp
+++ b/poincare/src/arc_sine.cpp
@@ -57,7 +57,7 @@ Expression ArcSine::shallowReduce(ExpressionNode::ReductionContext reductionCont
     }
   }
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   return Trigonometry::shallowReduceInverseFunction(*this, reductionContext);
 }
diff --git a/poincare/src/arc_tangent.cpp b/poincare/src/arc_tangent.cpp
index 153bf6820..1f33c83fe 100644
--- a/poincare/src/arc_tangent.cpp
+++ b/poincare/src/arc_tangent.cpp
@@ -56,7 +56,7 @@ Expression ArcTangent::shallowReduce(ExpressionNode::ReductionContext reductionC
     }
   }
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   return Trigonometry::shallowReduceInverseFunction(*this, reductionContext);
 }
diff --git a/poincare/src/ceiling.cpp b/poincare/src/ceiling.cpp
index fb8758ac5..285d63496 100644
--- a/poincare/src/ceiling.cpp
+++ b/poincare/src/ceiling.cpp
@@ -45,7 +45,7 @@ Expression Ceiling::shallowReduce(ExpressionNode::ReductionContext reductionCont
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.type() == ExpressionNode::Type::Constant) {
     Constant s = static_cast<Constant&>(c);
diff --git a/poincare/src/complex_argument.cpp b/poincare/src/complex_argument.cpp
index 059039054..e1b01e426 100644
--- a/poincare/src/complex_argument.cpp
+++ b/poincare/src/complex_argument.cpp
@@ -43,7 +43,7 @@ Expression ComplexArgument::shallowReduce(ExpressionNode::ReductionContext reduc
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   bool real = c.isReal(reductionContext.context());
   if (real) {
diff --git a/poincare/src/conjugate.cpp b/poincare/src/conjugate.cpp
index 29d07219d..b7c40c3ed 100644
--- a/poincare/src/conjugate.cpp
+++ b/poincare/src/conjugate.cpp
@@ -41,7 +41,7 @@ Expression Conjugate::shallowReduce(ExpressionNode::ReductionContext reductionCo
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.isReal(reductionContext.context())) {
     replaceWithInPlace(c);
diff --git a/poincare/src/cosine.cpp b/poincare/src/cosine.cpp
index 17b08ca1c..a47356564 100644
--- a/poincare/src/cosine.cpp
+++ b/poincare/src/cosine.cpp
@@ -43,7 +43,7 @@ Expression Cosine::shallowReduce(ExpressionNode::ReductionContext reductionConte
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   return Trigonometry::shallowReduceDirectFunction(*this, reductionContext);
 }
diff --git a/poincare/src/expression.cpp b/poincare/src/expression.cpp
index 80c72e736..52d43ad79 100644
--- a/poincare/src/expression.cpp
+++ b/poincare/src/expression.cpp
@@ -530,8 +530,10 @@ Expression Expression::ExpressionWithoutSymbols(Expression e, Context * context)
   return e;
 }
 
-Expression Expression::mapOnMatrixChild(ExpressionNode::ReductionContext reductionContext) {
-  assert(numberOfChildren() == 1 && childAtIndex(0).type() == ExpressionNode::Type::Matrix);
+Expression Expression::mapOnMatrixFirstChild(ExpressionNode::ReductionContext reductionContext) {
+  /* For now, the matrix child on which the mapping must be done  is always at
+   * the index 0. */
+  assert(childAtIndex(0).type() == ExpressionNode::Type::Matrix);
   Expression c = childAtIndex(0);
   Matrix matrix = Matrix::Builder();
   for (int i = 0; i < c.numberOfChildren(); i++) {
diff --git a/poincare/src/factorial.cpp b/poincare/src/factorial.cpp
index ab769b20f..f5f6c5a64 100644
--- a/poincare/src/factorial.cpp
+++ b/poincare/src/factorial.cpp
@@ -86,7 +86,7 @@ Expression Factorial::shallowReduce(ExpressionNode::ReductionContext reductionCo
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.type() == ExpressionNode::Type::Rational) {
     Rational r = c.convert<Rational>();
diff --git a/poincare/src/floor.cpp b/poincare/src/floor.cpp
index bc39a305c..4267a3abf 100644
--- a/poincare/src/floor.cpp
+++ b/poincare/src/floor.cpp
@@ -44,7 +44,7 @@ Expression Floor::shallowReduce(ExpressionNode::ReductionContext reductionContex
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.type() == ExpressionNode::Type::Constant) {
     Constant s = static_cast<Constant &>(c);
diff --git a/poincare/src/frac_part.cpp b/poincare/src/frac_part.cpp
index c49dd0357..4ca63fe07 100644
--- a/poincare/src/frac_part.cpp
+++ b/poincare/src/frac_part.cpp
@@ -41,7 +41,7 @@ Expression FracPart::shallowReduce(ExpressionNode::ReductionContext reductionCon
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.type() != ExpressionNode::Type::Rational) {
     return *this;
diff --git a/poincare/src/hyperbolic_trigonometric_function.cpp b/poincare/src/hyperbolic_trigonometric_function.cpp
index efb562c63..86815c938 100644
--- a/poincare/src/hyperbolic_trigonometric_function.cpp
+++ b/poincare/src/hyperbolic_trigonometric_function.cpp
@@ -16,7 +16,7 @@ Expression HyperbolicTrigonometricFunction::shallowReduce(ExpressionNode::Reduct
   }
   Expression c = childAtIndex(0);
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   return *this;
 }
diff --git a/poincare/src/imaginary_part.cpp b/poincare/src/imaginary_part.cpp
index 8c2987e4d..5dd188b58 100644
--- a/poincare/src/imaginary_part.cpp
+++ b/poincare/src/imaginary_part.cpp
@@ -33,7 +33,7 @@ Expression ImaginaryPart::shallowReduce(ExpressionNode::ReductionContext reducti
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.isReal(reductionContext.context())) {
     Expression result = Rational::Builder(0);
diff --git a/poincare/src/logarithm.cpp b/poincare/src/logarithm.cpp
index 004ec86f9..7d2387362 100644
--- a/poincare/src/logarithm.cpp
+++ b/poincare/src/logarithm.cpp
@@ -95,7 +95,7 @@ Expression CommonLogarithm::shallowReduce(ExpressionNode::ReductionContext reduc
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   Logarithm log = Logarithm::Builder(childAtIndex(0), Rational::Builder(10));
   replaceWithInPlace(log);
@@ -209,7 +209,7 @@ Expression Logarithm::shallowReduce(ExpressionNode::ReductionContext reductionCo
 
   // log(m) with m Matrix
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
 
   return *this;
diff --git a/poincare/src/naperian_logarithm.cpp b/poincare/src/naperian_logarithm.cpp
index 88522f1b3..cda1b199a 100644
--- a/poincare/src/naperian_logarithm.cpp
+++ b/poincare/src/naperian_logarithm.cpp
@@ -32,7 +32,7 @@ Expression NaperianLogarithm::shallowReduce(ExpressionNode::ReductionContext red
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   Logarithm l = Logarithm::Builder(c, Constant::Builder(UCodePointScriptSmallE));
   replaceWithInPlace(l);
diff --git a/poincare/src/real_part.cpp b/poincare/src/real_part.cpp
index 35140833b..60ccf90c4 100644
--- a/poincare/src/real_part.cpp
+++ b/poincare/src/real_part.cpp
@@ -33,7 +33,7 @@ Expression RealPart::shallowReduce(ExpressionNode::ReductionContext reductionCon
   }
   Expression c = childAtIndex(0);
   if (c.type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   if (c.isReal(reductionContext.context())) {
     replaceWithInPlace(c);
diff --git a/poincare/src/round.cpp b/poincare/src/round.cpp
index 041857a05..6895d0fec 100644
--- a/poincare/src/round.cpp
+++ b/poincare/src/round.cpp
@@ -51,7 +51,7 @@ Expression Round::shallowReduce(ExpressionNode::ReductionContext reductionContex
     return result;
   }
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   /* We reduce only round(Rational, Rational). We do not reduce
    * round(Float, Float) which is equivalent to what is done in approximate. */
diff --git a/poincare/src/sine.cpp b/poincare/src/sine.cpp
index f43482635..c7b5f902f 100644
--- a/poincare/src/sine.cpp
+++ b/poincare/src/sine.cpp
@@ -43,7 +43,7 @@ Expression Sine::shallowReduce(ExpressionNode::ReductionContext reductionContext
     }
   }
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
   return Trigonometry::shallowReduceDirectFunction(*this, reductionContext);
 }
diff --git a/poincare/src/tangent.cpp b/poincare/src/tangent.cpp
index 14f8bccd2..c731e78c8 100644
--- a/poincare/src/tangent.cpp
+++ b/poincare/src/tangent.cpp
@@ -47,7 +47,7 @@ Expression Tangent::shallowReduce(ExpressionNode::ReductionContext reductionCont
   }
 
   if (childAtIndex(0).type() == ExpressionNode::Type::Matrix) {
-    return mapOnMatrixChild(reductionContext);
+    return mapOnMatrixFirstChild(reductionContext);
   }
 
   Expression newExpression = Trigonometry::shallowReduceDirectFunction(*this, reductionContext);