diff --git a/mapytex/calculus/core/compute/multiply.py b/mapytex/calculus/core/compute/multiply.py
index d03e20b..2fc572c 100644
--- a/mapytex/calculus/core/compute/multiply.py
+++ b/mapytex/calculus/core/compute/multiply.py
@@ -15,7 +15,6 @@ from ..tree import Tree
 from ..MO.mo import MO, MOnumber, MOstr
 from ..MO.fraction import MOFraction
 from ..MO.monomial import MOstrPower, MOMonomial
-from .exceptions import MultiplyError
 from .filters import special_case
 
 multiply_doc = """ Multiply MOs
@@ -201,10 +200,10 @@ def mostr_mostrpower(left, right):
     >>> multiply(a, b)
     Traceback (most recent call last):
         ...
-    mapytex.calculus.core.compute.exceptions.MultiplyError: Can't multiply MOstr and MOstrPower if they don'thave same variable (got x and y)
+    NotImplementedError: Can't multiply MOstr and MOstrPower if they don'thave same variable (got x and y)
     """
     if left.variable != right.variable:
-        raise MultiplyError("Can't multiply MOstr and MOstrPower if they don't"
+        raise NotImplementedError("Can't multiply MOstr and MOstrPower if they don't"
                 f"have same variable (got {left.variable} and {right.variable})")
     return MOstrPower(left.variable, right.power.value+1)
 
@@ -222,13 +221,35 @@ def mostr_mostrpower(left, right):
     >>> multiply(a, b)
     Traceback (most recent call last):
         ...
-    mapytex.calculus.core.compute.exceptions.MultiplyError: Can't multiply MOstr and MOstrPower if they don'thave same variable (got x and y)
+    NotImplementedError: Can't multiply MOstr and MOstrPower if they don'thave same variable (got x and y)
     """
     if left.variable != right.variable:
-        raise MultiplyError("Can't multiply MOstr and MOstrPower if they don't"
+        raise NotImplementedError("Can't multiply MOstr and MOstrPower if they don't"
                 f"have same variable (got {left.variable} and {right.variable})")
     return MOstrPower(left.variable, left.power.value+1)
 
+@multiply.register(MOstr, MOstr)
+@special_case(multiply_filter)
+def mostr_mostr(left, right):
+    """ Multiply a MOstr and a MOstr
+
+    :example:
+    >>> a = MOstr('x')
+    >>> b = MOstr('x')
+    >>> multiply(a, b)
+    <MOstrPower x^2>
+    >>> a = MOstr('y')
+    >>> b = MOstr('x')
+    >>> multiply(a, b)
+    Traceback (most recent call last):
+        ...
+    NotImplementedError: Can't multiply MOstr and MOstr if they don'thave same variable (got y and x)
+    """
+    if left.variable != right.variable:
+        raise NotImplementedError("Can't multiply MOstr and MOstr if they don't"
+                f"have same variable (got {left.variable} and {right.variable})")
+    return MOstrPower(left.variable, 2)
+
 @multiply.register(MOstrPower, MOstrPower)
 @special_case(multiply_filter)
 def mostr_mostrpower(left, right):
@@ -247,14 +268,157 @@ def mostr_mostrpower(left, right):
     >>> multiply(a, b)
     Traceback (most recent call last):
         ...
-    mapytex.calculus.core.compute.exceptions.MultiplyError: Can't multiply MOstr and MOstrPower if they don'thave same variable (got x and y)
+    NotImplementedError: Can't multiply MOstrPower and MOstrPower if they don'thave same variable (got x and y)
     """
     if left.variable != right.variable:
-        raise MultiplyError("Can't multiply MOstr and MOstrPower if they don't"
+        raise NotImplementedError("Can't multiply MOstrPower and MOstrPower if they don't"
                 f"have same variable (got {left.variable} and {right.variable})")
     power = Tree("+", left.power, right.power)
     return Tree("^", left.variable, power)
 
+@multiply.register(MOstrPower, MOMonomial)
+@special_case(multiply_filter)
+def mostr_momonomial(left, right):
+    """ Multiply a MOstrPower and a MOMonomial
+
+    >>> a = MOstrPower('x', 2)
+    >>> b = MOMonomial(2, 'x', 4)
+    >>> print(multiply(a, b))
+    *
+     > 2
+     > ^
+     | > x
+     | > +
+     | | > 2
+     | | > 4
+    >>> a = MOstrPower('x', 2)
+    >>> b = MOMonomial(2, 'y', 4)
+    >>> multiply(a, b)
+    Traceback (most recent call last):
+        ...
+    NotImplementedError: Can't multiply MOstrPower and Monomial if they don'thave same variable (got x and y)
+    """
+    if left.variable != right.variable:
+        raise NotImplementedError("Can't multiply MOstrPower and Monomial if they don't"
+                f"have same variable (got {left.variable} and {right.variable})")
+    power = Tree("+", left.power, right.power)
+    monome = Tree("^", left.variable, power)
+    return Tree("*", right.coefficient, monome)
+
+@multiply.register(MOMonomial, MOstrPower)
+@special_case(multiply_filter)
+def momonomial_mostr(left, right):
+    """ Multiply a MOMonomial and a MOstrPower
+
+    >>> a = MOMonomial(2, 'x', 4)
+    >>> b = MOstrPower('x', 2)
+    >>> print(multiply(a, b))
+    *
+     > 2
+     > ^
+     | > x
+     | > +
+     | | > 4
+     | | > 2
+    >>> a = MOMonomial(2, 'y', 4)
+    >>> b = MOstrPower('x', 2)
+    >>> multiply(a, b)
+    Traceback (most recent call last):
+        ...
+    NotImplementedError: Can't multiply MOstrPower and Monomial if they don'thave same variable (got y and x)
+
+    """
+    if left.variable != right.variable:
+        raise NotImplementedError("Can't multiply MOstrPower and Monomial if they don't"
+                f"have same variable (got {left.variable} and {right.variable})")
+    power = Tree("+", left.power, right.power)
+    monome = Tree("^", left.variable, power)
+    return Tree("*", left.coefficient, monome)
+
+@multiply.register(MOstr, MOMonomial)
+@special_case(multiply_filter)
+def mostr_momonomial(left, right):
+    """ Multiply a MOstr and a MOMonomial
+
+    >>> a = MOstr('x')
+    >>> b = MOMonomial(2, 'x', 4)
+    >>> print(multiply(a, b))
+    *
+     > 2
+     > ^
+     | > x
+     | > 5
+    >>> a = MOstr('x')
+    >>> b = MOMonomial(2, 'y', 4)
+    >>> multiply(a, b)
+    Traceback (most recent call last):
+        ...
+    NotImplementedError: Can't multiply MOstr and Monomial if they don'thave same variable (got x and y)
+    """
+    if left.variable != right.variable:
+        raise NotImplementedError("Can't multiply MOstr and Monomial if they don't"
+                f"have same variable (got {left.variable} and {right.variable})")
+    return MOMonomial(right.coefficient, right.variable, right.power.value+1)
+
+@multiply.register(MOMonomial, MOstr)
+@special_case(multiply_filter)
+def momonomial_mostr(left, right):
+    """ Multiply a MOMonomial and a MOstr
+
+    >>> a = MOMonomial(2, 'x', 4)
+    >>> b = MOstr('x')
+    >>> print(multiply(a, b))
+    *
+     > 2
+     > ^
+     | > x
+     | > 5
+    >>> a = MOMonomial(2, 'y', 4)
+    >>> b = MOstr('x')
+    >>> multiply(a, b)
+    Traceback (most recent call last):
+        ...
+    NotImplementedError: Can't multiply MOstr and Monomial if they don'thave same variable (got y and x)
+
+    """
+    if left.variable != right.variable:
+        raise NotImplementedError("Can't multiply MOstr and Monomial if they don't"
+                f"have same variable (got {left.variable} and {right.variable})")
+    return MOMonomial(left.coefficient, left.variable, left.power.value+1)
+
+@multiply.register(MOMonomial, MOMonomial)
+@special_case(multiply_filter)
+def momonomial_momonomial(left, right):
+    """ Multiply a MOMonomial and a MOMonomial
+
+    >>> a = MOMonomial(2, 'x', 4)
+    >>> b = MOMonomial(3, 'x', 2)
+    >>> print(multiply(a, b))
+    *
+     > *
+     | > 2
+     | > 3
+     > ^
+     | > x
+     | > +
+     | | > 4
+     | | > 2
+    >>> a = MOMonomial(2, 'y', 4)
+    >>> b = MOMonomial(3, 'x', 2)
+    >>> multiply(a, b)
+    Traceback (most recent call last):
+        ...
+    NotImplementedError: Can't multiply MOMonomial and Monomial if they don'thave same variable (got y and x)
+
+    """
+    if left.variable != right.variable:
+        raise NotImplementedError("Can't multiply MOMonomial and Monomial if they don't"
+                f"have same variable (got {left.variable} and {right.variable})")
+    powers = Tree("+", left.power, right.power)
+    monome = Tree("^", left.variable, powers)
+    coefs = Tree("*", left.coefficient, right.coefficient)
+    return Tree("*", coefs, monome)
+
 # -----------------------------
 # Reglages pour 'vim'
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