diff --git a/poincare/Makefile b/poincare/Makefile
index c7144dd49..b4a1c4f5b 100644
--- a/poincare/Makefile
+++ b/poincare/Makefile
@@ -4,7 +4,7 @@ objs += $(addprefix poincare/src/,\
   binary_operation.o\
   commutative_operation.o\
   context.o\
-  cosinus.o\
+  cosine.o\
   expression.o\
   expression_lexer.o\
   expression_parser.o\
@@ -15,7 +15,7 @@ objs += $(addprefix poincare/src/,\
   leaf_expression.o\
   power.o\
   product.o\
-  sinus.o\
+  sine.o\
   subtraction.o\
   symbol.o\
   tangent.o\
@@ -40,6 +40,7 @@ tests += $(addprefix poincare/test/,\
   product.cpp\
   simplify.cpp\
   simplify_addition_integer.cpp\
+  trigo.cpp\
   subtraction.cpp\
 )
 
diff --git a/poincare/include/poincare.h b/poincare/include/poincare.h
index 4b89926c0..21b774e7c 100644
--- a/poincare/include/poincare.h
+++ b/poincare/include/poincare.h
@@ -3,7 +3,7 @@
 
 #include <poincare/addition.h>
 #include <poincare/context.h>
-#include <poincare/cosinus.h>
+#include <poincare/cosine.h>
 #include <poincare/expression.h>
 #include <poincare/float.h>
 #include <poincare/fraction.h>
@@ -11,7 +11,7 @@
 #include <poincare/integer.h>
 #include <poincare/power.h>
 #include <poincare/product.h>
-#include <poincare/sinus.h>
+#include <poincare/sine.h>
 #include <poincare/subtraction.h>
 #include <poincare/symbol.h>
 #include <poincare/tangent.h>
diff --git a/poincare/include/poincare/cosine.h b/poincare/include/poincare/cosine.h
new file mode 100644
index 000000000..31f376375
--- /dev/null
+++ b/poincare/include/poincare/cosine.h
@@ -0,0 +1,14 @@
+#ifndef POINCARE_COSINE_H
+#define POINCARE_COSINE_H
+
+#include <poincare/function.h>
+
+class Cosine : public Function {
+  public:
+    Cosine(Expression * arg, bool clone_arg=true): Function(arg, (char*) "cos", clone_arg) {}
+    float approximate(Context& context) override;
+    Type type() override;
+    Expression * clone() override;
+};
+
+#endif
diff --git a/poincare/include/poincare/cosinus.h b/poincare/include/poincare/cosinus.h
deleted file mode 100644
index f23e66e4c..000000000
--- a/poincare/include/poincare/cosinus.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef POINCARE_COSINUS_H
-#define POINCARE_COSINUS_H
-
-#include <poincare/function.h>
-
-class Cosinus : public Function {
-  public:
-    Cosinus(Expression * arg, bool clone_arg=true): Function(arg, (char*) "cos", clone_arg) {}
-    float approximate(Context& context) override;
-    Type type() override;
-    Expression * clone() override;
-};
-
-#endif
diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index 44dcd345f..cedb2ec46 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -10,13 +10,13 @@ class Expression {
   public:
     enum class Type : uint8_t {
       Addition,
-      Cosinus,
+      Cosine,
       Float,
       Fraction,
       Integer,
       Power,
       Product,
-      Sinus,
+      Sine,
       Subtraction,
       Symbol,
       Tangent,
diff --git a/poincare/include/poincare/sine.h b/poincare/include/poincare/sine.h
new file mode 100644
index 000000000..fe53563a0
--- /dev/null
+++ b/poincare/include/poincare/sine.h
@@ -0,0 +1,14 @@
+#ifndef POINCARE_SINE_H
+#define POINCARE_SINE_H
+
+#include <poincare/function.h>
+
+class Sine : public Function {
+  public:
+    Sine(Expression * arg, bool clone_arg=true): Function(arg, (char*) "sin", clone_arg) {}
+    float approximate(Context& context) override;
+    Type type() override;
+    Expression * clone() override;
+};
+
+#endif
diff --git a/poincare/include/poincare/sinus.h b/poincare/include/poincare/sinus.h
deleted file mode 100644
index a970aac09..000000000
--- a/poincare/include/poincare/sinus.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef POINCARE_SINUS_H
-#define POINCARE_SINUS_H
-
-#include <poincare/function.h>
-
-class Sinus : public Function {
-  public:
-    Sinus(Expression * arg, bool clone_arg=true): Function(arg, (char*) "sin", clone_arg) {}
-    float approximate(Context& context) override;
-    Type type() override;
-    Expression * clone() override;
-};
-
-#endif
diff --git a/poincare/src/addition.cpp b/poincare/src/addition.cpp
index cb4080b33..15795ee7b 100644
--- a/poincare/src/addition.cpp
+++ b/poincare/src/addition.cpp
@@ -14,6 +14,5 @@ float Addition::operateApproximatevelyOn(float a, float b) {
 }
 
 ExpressionLayout * Addition::createLayout(ExpressionLayout * parent) {
-  //FIXME: There can be more than two operands now! :-)
-  return new HorizontalLayout(parent, operand(0), '+', operand(1));
+  return new HorizontalLayout(parent, m_operands, m_numberOfOperands, '+');
 }
diff --git a/poincare/src/commutative_operation.cpp b/poincare/src/commutative_operation.cpp
index 929908076..37252e0a0 100644
--- a/poincare/src/commutative_operation.cpp
+++ b/poincare/src/commutative_operation.cpp
@@ -30,6 +30,7 @@ int CommutativeOperation::numberOfOperands() {
 }
 
 Expression * CommutativeOperation::operand(int i) {
+  assert(i < m_numberOfOperands);
   return m_operands[i];
 }
 
diff --git a/poincare/src/cosine.cpp b/poincare/src/cosine.cpp
new file mode 100644
index 000000000..8fafad923
--- /dev/null
+++ b/poincare/src/cosine.cpp
@@ -0,0 +1,15 @@
+#include <poincare/cosine.h>
+#include "layout/horizontal_layout.h"
+
+Expression * Cosine::clone() {
+  return new Cosine(m_arg, true);
+}
+
+Expression::Type Cosine::type() {
+  return Expression::Type::Cosine;
+}
+
+float Cosine::approximate(Context& context) {
+  // FIXME: use cosine obviously.
+  return m_arg->approximate(context);
+}
diff --git a/poincare/src/cosinus.cpp b/poincare/src/cosinus.cpp
deleted file mode 100644
index 070b82a2a..000000000
--- a/poincare/src/cosinus.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-#include <poincare/cosinus.h>
-#include "layout/horizontal_layout.h"
-
-Expression * Cosinus::clone() {
-  return new Cosinus(m_arg, true);
-}
-
-Expression::Type Cosinus::type() {
-  return Expression::Type::Cosinus;
-}
-
-float Cosinus::approximate(Context& context) {
-  // FIXME: use cosinus obviously.
-  return m_arg->approximate(context);
-}
diff --git a/poincare/src/expression_lexer.l b/poincare/src/expression_lexer.l
index 008e5fca5..26a2dffdc 100644
--- a/poincare/src/expression_lexer.l
+++ b/poincare/src/expression_lexer.l
@@ -42,10 +42,10 @@ class Expression;
 %%
 
 [0-9]+ { yylval->string = yytext; return(INTEGER); }
-[A-Za-z]+ { yylval->string = yytext; return(SYMBOL); }
-sin {return(SINUS);}
-cos {return(COSINUS);}
+sin {return(SINE);}
+cos {return(COSINE);}
 tan {return(TANGENT);}
+[A-Za-z]+ { yylval->string = yytext; return(SYMBOL); }
 \+ { return(PLUS); }
 \- { return(MINUS); }
 \* { return(MULTIPLY); }
diff --git a/poincare/src/expression_parser.y b/poincare/src/expression_parser.y
index bb3dd2b14..43c501e64 100644
--- a/poincare/src/expression_parser.y
+++ b/poincare/src/expression_parser.y
@@ -54,8 +54,8 @@ void poincare_expression_yyerror(void * scanner, Expression ** expressionOutput,
 %token MULTIPLY
 %token DIVIDE
 %token POW
-%token SINUS
-%token COSINUS
+%token SINE
+%token COSINE
 %token TANGENT
 %token LEFT_PARENTHESIS
 %token RIGHT_PARENTHESIS
@@ -88,8 +88,8 @@ exp:
   | exp DIVIDE exp   { Expression * terms[2] = {$1,$3}; $$ = new Fraction(terms, false); }
   | exp POW exp      { Expression * terms[2] = {$1,$3}; $$ = new Power(terms, false); }
   | LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = $2; }
-  | SINUS LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Sinus($3); }
-  | COSINUS LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Cosinus($3); }
+  | SINE LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Sine($3); }
+  | COSINE LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Cosine($3); }
   | TANGENT LEFT_PARENTHESIS exp RIGHT_PARENTHESIS     { $$ = new Tangent($3); }
 ;
 
diff --git a/poincare/src/layout/horizontal_layout.cpp b/poincare/src/layout/horizontal_layout.cpp
index 0ba763f4b..eebc343b0 100644
--- a/poincare/src/layout/horizontal_layout.cpp
+++ b/poincare/src/layout/horizontal_layout.cpp
@@ -1,29 +1,28 @@
 extern "C" {
-#include <kandinsky.h>
 #include <assert.h>
+#include <kandinsky.h>
+#include <stdlib.h>
 }
 #include "horizontal_layout.h"
 #include "string_layout.h"
 
-HorizontalLayout::HorizontalLayout(ExpressionLayout * parent, int number_of_operands, Expression ** operands, char symbol) {
-  m_number_of_operands = number_of_operands;
-  // FIXME: This implementation is not optimal as the operator layout is created and stored a lot of times.
-  // The reason for this is how the layouts are drawn.
-  m_children_layouts = (ExpressionLayout **)malloc((2*m_number_of_operands-)*sizeof(ExpressionLayout *));
-  m_operator_layout = new StringLayout(this, string, 1);
+HorizontalLayout::HorizontalLayout(ExpressionLayout * parent, Expression ** operands,int number_of_operands, char symbol) : ExpressionLayout(parent) {
+  assert(number_of_operands > 0);
+  m_number_of_children = 2*number_of_operands-1;
+  m_children_layouts = (ExpressionLayout **)malloc(m_number_of_children*sizeof(ExpressionLayout *));
   char string[2] = {symbol, '\0'};
-  for (int i=1; i<m_number_of_operands; i++) {
-    m_operands[2*i-1] = m_operator_layout;
-    m_operands[2*i] = operands[i]->createLayout();
+  m_children_layouts[0] = operands[0]->createLayout(this);
+  for (int i=1; i<number_of_operands; i++) {
+    m_children_layouts[2*i-1] = new StringLayout(this, string, 1);
+    m_children_layouts[2*i] = operands[i]->createLayout(this);
   }
 }
 
 HorizontalLayout::~HorizontalLayout() {
-  for (int i(0); i<m_numberOfOperands; i++) {
-    delete m_operands[2*i];
+  for (int i=0; i<m_number_of_children; i++) {
+    delete m_children_layouts[i];
   }
-  free(m_operands);
-  delete m_operator_layout;
+  free(m_children_layouts);
 }
 
 void HorizontalLayout::render(KDPoint point) { }
@@ -42,23 +41,25 @@ KDSize HorizontalLayout::computeSize() {
 }
 
 ExpressionLayout * HorizontalLayout::child(uint16_t index) {
-  if (index >= 2*m_number_of_operands) {
+  assert(index <= m_number_of_children);
+  if (index < m_number_of_children) {
+    return m_children_layouts[index];
+  } else {
     return nullptr;
   }
-  return m_children_layouts[index];
 }
 
 KDPoint HorizontalLayout::positionOfChild(ExpressionLayout * child) {
   KDPoint position = (KDPoint){.x = 0, .y = 0};
   uint16_t index = 0;
-  for (int i=0;i<3;i++) {
-    if (m_children[i] == child) {
+  for (int i=0;i<m_number_of_children;i++) {
+    if (m_children_layouts[i] == child) {
       index = i;
       break;
     }
   }
   if (index > 0) {
-    ExpressionLayout * previousChild = m_children[index-1];
+    ExpressionLayout * previousChild = m_children_layouts[index-1];
     assert(previousChild != nullptr);
     position.x = previousChild->origin().x + previousChild->size().width;
   }
diff --git a/poincare/src/layout/horizontal_layout.h b/poincare/src/layout/horizontal_layout.h
index 4482aca87..0ee133f5c 100644
--- a/poincare/src/layout/horizontal_layout.h
+++ b/poincare/src/layout/horizontal_layout.h
@@ -6,7 +6,7 @@
 
 class HorizontalLayout : public ExpressionLayout {
   public:
-    HorizontalLayout(ExpressionLayout * parent, int number_of_operands, Expression ** operands, char symbol);
+    HorizontalLayout(ExpressionLayout * parent, Expression ** operands, int number_of_children, char symbol);
     ~HorizontalLayout();
   protected:
     void render(KDPoint point) override;
@@ -14,9 +14,8 @@ class HorizontalLayout : public ExpressionLayout {
     ExpressionLayout * child(uint16_t index) override;
     KDPoint positionOfChild(ExpressionLayout * child) override;
   private:
-    int m_number_of_operands;
+    int m_number_of_children;
     ExpressionLayout ** m_children_layouts;
-    ExpressionLayout * m_operator_layout;
 };
 
 #endif
diff --git a/poincare/src/product.cpp b/poincare/src/product.cpp
index fc888bfd8..36c93dcba 100644
--- a/poincare/src/product.cpp
+++ b/poincare/src/product.cpp
@@ -17,6 +17,5 @@ Expression::Type Product::type() {
 }
 
 ExpressionLayout * Product::createLayout(ExpressionLayout * parent) {
-  //FIXME: There can be more than two factors now! :-)
-  return new HorizontalLayout(parent, operand(0), '*', operand(1));
+  return new HorizontalLayout(parent, m_operands, m_numberOfOperands, '*');
 }
diff --git a/poincare/src/sine.cpp b/poincare/src/sine.cpp
new file mode 100644
index 000000000..fb3d7003c
--- /dev/null
+++ b/poincare/src/sine.cpp
@@ -0,0 +1,15 @@
+#include <poincare/sine.h>
+#include "layout/horizontal_layout.h"
+
+Expression * Sine::clone() {
+  return new Sine(m_arg, true);
+}
+
+Expression::Type Sine::type() {
+  return Expression::Type::Sine;
+}
+
+float Sine::approximate(Context& context) {
+  // FIXME: use sine obviously.
+  return m_arg->approximate(context);
+}
diff --git a/poincare/src/sinus.cpp b/poincare/src/sinus.cpp
deleted file mode 100644
index 9a73559a3..000000000
--- a/poincare/src/sinus.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-#include <poincare/sinus.h>
-#include "layout/horizontal_layout.h"
-
-Expression * Sinus::clone() {
-  return new Sinus(m_arg, true);
-}
-
-Expression::Type Sinus::type() {
-  return Expression::Type::Sinus;
-}
-
-float Sinus::approximate(Context& context) {
-  // FIXME: use sinus obviously.
-  return m_arg->approximate(context);
-}
diff --git a/poincare/src/subtraction.cpp b/poincare/src/subtraction.cpp
index 7f82f02db..448553f2a 100644
--- a/poincare/src/subtraction.cpp
+++ b/poincare/src/subtraction.cpp
@@ -14,5 +14,5 @@ Expression::Type Subtraction::type() {
 }
 
 ExpressionLayout * Subtraction::createLayout(ExpressionLayout * parent) {
-  return new HorizontalLayout(parent, m_operands[0], '-', m_operands[1]);
+  return new HorizontalLayout(parent, m_operands, 2, '-');
 }
diff --git a/poincare/test/trigo.cpp b/poincare/test/trigo.cpp
new file mode 100644
index 000000000..700ac5b64
--- /dev/null
+++ b/poincare/test/trigo.cpp
@@ -0,0 +1,21 @@
+#include <quiz.h>
+#include <poincare.h>
+#include <assert.h>
+
+QUIZ_CASE(poincare_parse_trigo) {
+  {
+    Expression * e = Expression::parse("sin(0)");
+    Expression * e2 = e->simplify();
+    assert(e2->type() == Expression::Type::Sine);
+  }
+  {
+    Expression * e = Expression::parse("cos(0)");
+    Expression * e2 = e->simplify();
+    assert(e2->type() == Expression::Type::Cosine);
+  }
+  {
+    Expression * e = Expression::parse("tan(0)");
+    Expression * e2 = e->simplify();
+    assert(e2->type() == Expression::Type::Tangent);
+  }
+}