diff --git a/mapytex/calculus/core/compute/add.py b/mapytex/calculus/core/compute/add.py
index b566140..691d16a 100644
--- a/mapytex/calculus/core/compute/add.py
+++ b/mapytex/calculus/core/compute/add.py
@@ -10,13 +10,14 @@
 Adding MO
 """
 
+from functools import wraps
 from multipledispatch import Dispatcher
 from ..tree import Tree
 from ..MO.mo import MO, MOnumber
 from ..MO.fraction import MOFraction
 from .exceptions import AddError
 from .arithmetic import lcm
-from .type_filter import args_are
+from .filters import special_case
 
 add_doc = """ Adding MOs
 
@@ -25,9 +26,36 @@ add_doc = """ Adding MOs
 :return: Tree or MO
 
 """
+
 add = Dispatcher("add", doc=add_doc)
 
+def add_filter(left, right):
+    """ Automatic add on MO
+
+    :param left: MO
+    :param right: MO
+    :returns: MO if it is a special case, nothing other wise
+
+    >>> a = MOnumber(0)
+    >>> b = MOFraction(1, 2)
+    >>> add(a, b)
+    <MOFraction 1 / 2>
+    >>> add(b, a)
+    <MOFraction 1 / 2>
+    """
+    try:
+        if left == 0:
+            return right
+    except TypeError:
+        pass
+    try:
+        if right == 0:
+            return left
+    except TypeError:
+        pass
+
 @add.register(MOnumber, MOnumber)
+@special_case(add_filter)
 def monumber_monumber(left, right):
     """ Simply add MO value
 
@@ -40,6 +68,7 @@ def monumber_monumber(left, right):
     return MO.factory(left.value + right.value)
 
 @add.register(MOnumber, MOFraction)
+@special_case(add_filter)
 def monumber_mofraction(left, right):
     """ Return a tree with the MOnumber transformed into a MOFraction
 
@@ -58,6 +87,7 @@ def monumber_mofraction(left, right):
     return Tree("+", left_fraction, right)
 
 @add.register(MOFraction, MOnumber)
+@special_case(add_filter)
 def mofraction_monumber(left, right):
     """ Return a tree with the MOnumber transformed into a MOFraction
 
@@ -76,6 +106,7 @@ def mofraction_monumber(left, right):
     return Tree("+", left, right_fraction)
 
 @add.register(MOFraction, MOFraction)
+@special_case(add_filter)
 def mofraction_mofraction(left, right):
     """ 3 differents cases:
 
diff --git a/mapytex/calculus/core/compute/divide.py b/mapytex/calculus/core/compute/divide.py
index 025083f..ec9afb7 100644
--- a/mapytex/calculus/core/compute/divide.py
+++ b/mapytex/calculus/core/compute/divide.py
@@ -15,7 +15,7 @@ from ..tree import Tree
 from ..MO.mo import MO, MOnumber
 from ..MO.fraction import MOFraction
 from .exceptions import DivideError
-from .type_filter import args_are
+from .filters import special_case
 
 divide_doc = """ Dividing MOs
 
@@ -27,7 +27,42 @@ divide_doc = """ Dividing MOs
 
 divide = Dispatcher("divide", doc=divide_doc)
 
+def divide_filter(left, right):
+    """ Automatic divide on MO
+
+    >>> a = MOnumber(4)
+    >>> b = MOnumber(1)
+    >>> divide(a, b)
+    <MOnumber 4>
+    >>> a = MOnumber(0)
+    >>> b = MOnumber(1)
+    >>> divide(a, b)
+    <MOnumber 0>
+    >>> a = MOnumber(4)
+    >>> b = MOnumber(0)
+    >>> divide(a, b)
+    Traceback (most recent call last):
+        ...
+    mapytex.calculus.core.compute.exceptions.DivideError: Division by zero
+    """
+    try:
+        if left == 0:
+            return left
+    except TypeError:
+        pass
+    try:
+        if right == 1:
+            return left
+    except TypeError:
+        pass
+    try:
+        if right == 0:
+            raise DivideError("Division by zero")
+    except TypeError:
+        pass
+
 @divide.register(MOnumber, MOnumber)
+@special_case(divide_filter)
 def monumber_monumber(left, right):
     """ Divide 2 monumbers and return a MOFraction
 
@@ -39,6 +74,7 @@ def monumber_monumber(left, right):
     return MOFraction(left, right)
 
 @divide.register(MOnumber, MOFraction)
+@special_case(divide_filter)
 def monumber_mofraction(left, right):
     """ Divide a monumber and a mofraction by inverting MOFraction
 
@@ -63,6 +99,7 @@ def monumber_mofraction(left, right):
     return Tree("*", left, right.inverse())
 
 @divide.register(MOFraction, MOnumber)
+@special_case(divide_filter)
 def mofraction_monumber(left, right):
     """ Divide a monumber and a mofraction by inverting MOnumber
 
@@ -82,6 +119,7 @@ def mofraction_monumber(left, right):
     return Tree("*", left, right_fraction)
 
 @divide.register(MOFraction, MOFraction)
+@special_case(divide_filter)
 def mofraction_mofraction(left, right):
     """ Divide two mofractions by inverting right MOFraction
 
@@ -99,37 +137,6 @@ def mofraction_mofraction(left, right):
     """
     return Tree("*", left, right.inverse())
 
-#def divide(left, right):
-#    """ Perform the addition of left and right
-#
-#    :param left: left MO
-#    :param right: right MO
-#    :returns: Tree or MO
-#
-#    >>> a = MOnumber(4)
-#    >>> b = MOnumber(6)
-#    >>> divide(a, b)
-#    <MOFraction 4 / 6>
-#    >>> b = MOnumber(0)
-#    >>> divide(a, b)
-#    Traceback (most recent call last):
-#        ...
-#    mapytex.calculus.core.compute.exceptions.DivideError: Division by zero
-#
-#    """
-#    try:
-#        right.value
-#    except AttributeError:
-#        pass
-#    else:
-#        if right.value == 0:
-#            raise DivideError("Division by zero")
-#
-#    if right.value == 1:
-#        return left
-#
-#    return MULFUNCTIONS[(type(left), type(right))](left, right)
-
 # -----------------------------
 # Reglages pour 'vim'
 # vim:set autoindent expandtab tabstop=4 shiftwidth=4:
diff --git a/mapytex/calculus/core/compute/type_filter.py b/mapytex/calculus/core/compute/filters.py
similarity index 76%
rename from mapytex/calculus/core/compute/type_filter.py
rename to mapytex/calculus/core/compute/filters.py
index 64e5417..fd4a2c8 100644
--- a/mapytex/calculus/core/compute/type_filter.py
+++ b/mapytex/calculus/core/compute/filters.py
@@ -36,7 +36,22 @@ def args_are(left_type, right_type):
         return filtered_func
     return type_filter
 
+def special_case(filter):
+    """ Decorate operation to filter special cases before call the function
 
+    :param filter: (MO, MO) -> MO or Tree
+    :returns: decorator
+
+    """
+    def decorator(func):
+        @wraps(func)
+        def _func(left, right):
+            ans = filter(left, right)
+            if ans is None:
+                return func(left, right)
+            return ans
+        return _func
+    return decorator
 
 # -----------------------------
 # Reglages pour 'vim'
diff --git a/mapytex/calculus/core/compute/multiply.py b/mapytex/calculus/core/compute/multiply.py
index 079b07d..86612d9 100644
--- a/mapytex/calculus/core/compute/multiply.py
+++ b/mapytex/calculus/core/compute/multiply.py
@@ -16,7 +16,7 @@ from ..MO.mo import MO, MOnumber, MOstr
 from ..MO.fraction import MOFraction
 from ..MO.monomial import MOMonomial
 from .exceptions import MultiplyError
-from .type_filter import args_are
+from .filters import special_case
 
 multiply_doc = """ Multiply MOs
 
@@ -28,7 +28,48 @@ multiply_doc = """ Multiply MOs
 
 multiply = Dispatcher("multiply", doc=multiply_doc)
 
+def multiply_filter(left, right):
+    """ Automatic multiply on MO
+
+    :param left: MO
+    :param right: MO
+    :returns: MO if it is a special case, nothing other wise
+
+    >>> a = MOnumber(1)
+    >>> b = MOFraction(1, 2)
+    >>> multiply(a, b)
+    <MOFraction 1 / 2>
+    >>> multiply(b, a)
+    <MOFraction 1 / 2>
+    >>> a = MOnumber(0)
+    >>> b = MOFraction(1, 2)
+    >>> multiply(a, b)
+    <MOnumber 0>
+    """
+    try:
+        if left == 0:
+            return left
+    except TypeError:
+        pass
+    try:
+        if right == 0:
+            return right
+    except TypeError:
+        pass
+
+    try:
+        if left == 1:
+            return right
+    except TypeError:
+        pass
+    try:
+        if right == 1:
+            return left
+    except TypeError:
+        pass
+
 @multiply.register(MOnumber, MOnumber)
+@special_case(multiply_filter)
 def monumber_monumber(left, right):
     """ Simply multiply values
 
@@ -41,6 +82,7 @@ def monumber_monumber(left, right):
     return MO.factory(left.value * right.value)
 
 @multiply.register(MOnumber, MOFraction)
+@special_case(multiply_filter)
 def monumber_mofraction(left, right):
     """ Return division Tree with on the numertor MOnumber times numerator of MOFraction
 
@@ -67,6 +109,7 @@ def monumber_mofraction(left, right):
     return Tree("/", num, right._denominator)
 
 @multiply.register(MOFraction, MOnumber)
+@special_case(multiply_filter)
 def mofraction_monumber(left, right):
     """ Return division Tree with on the numertor MOnumber times numerator of MOFraction
 
@@ -83,6 +126,7 @@ def mofraction_monumber(left, right):
     return Tree("/", num, left._denominator)
 
 @multiply.register(MOFraction, MOFraction)
+@special_case(multiply_filter)
 def mofraction_mofraction(left, right):
     """ Multiply two mofractions (numertors together and denominators together)
 
@@ -102,6 +146,7 @@ def mofraction_mofraction(left, right):
     return Tree("/", num, denom)
 
 @multiply.register((MOnumber, MOFraction), MOstr)
+@special_case(multiply_filter)
 def moscalar_mostr(left, right):
     """ Multiply a scalar with a letter to create a MOMonomial
 
@@ -116,6 +161,7 @@ def moscalar_mostr(left, right):
     return MOMonomial(left, right)
 
 @multiply.register(MOstr, (MOnumber, MOFraction))
+@special_case(multiply_filter)
 def mostr_moscalar(left, right):
     """ Multiply a scalar with a letter to create a MOMonomial
 
@@ -130,6 +176,7 @@ def mostr_moscalar(left, right):
     return MOMonomial(right, left)
 
 @multiply.register((MOnumber, MOFraction), MOMonomial)
+@special_case(multiply_filter)
 def moscalar_monomonial(left, right):
     """ Multiply a scalar with a monomial