diff --git a/mapytex/calculus/core/compute/add.py b/mapytex/calculus/core/compute/add.py
index 55a6c6a..bf2cdde 100644
--- a/mapytex/calculus/core/compute/add.py
+++ b/mapytex/calculus/core/compute/add.py
@@ -717,6 +717,113 @@ def mopolynomial_mopolynomial(left, right):
 
     return Tree.from_list("+", list(merge_monomials.values())[::-1])
 
+@add.register(MOstr, MOMonomial)
+@special_case(add_filter)
+def mostr_momonomial(left, right):
+    """ Add a str to a Monomial
+
+    :example:
+    >>> a = MOstr("x")
+    >>> b = MOMonomial(2, "x")
+    >>> print(add(a, b))
+    *
+     > +
+     | > 1
+     | > 2
+     > x
+    """
+    if right.power != 1:
+        raise NotImplementedError("Monomial is more than deg 1")
+    add_scal = Tree("+", 1, right.coefficient)
+    return Tree("*", add_scal, left)
+
+@add.register(MOMonomial, MOstr)
+@special_case(add_filter)
+def momonomial_mostr(left, right):
+    """ Add a str to a Monomial
+
+    :example:
+    >>> a = MOMonomial(2, "x")
+    >>> b = MOstr("x")
+    >>> print(add(a, b))
+    *
+     > +
+     | > 2
+     | > 1
+     > x
+    """
+    if left.power != 1:
+        raise NotImplementedError("Monomial is more than deg 1")
+    add_scal = Tree("+", left.coefficient, 1)
+    return Tree("*", add_scal, right)
+
+@add.register(MOstrPower, MOMonomial)
+@special_case(add_filter)
+def mostrpower_momonomial(left, right):
+    """ Add a strpower to a Monomial
+
+    :example:
+    >>> a = MOstrPower("x", 2)
+    >>> b = MOMonomial(3, "x", 2)
+    >>> print(add(a, b))
+    *
+     > +
+     | > 1
+     | > 3
+     > ^
+     | > x
+     | > 2
+    """
+    if right.power != left.power:
+        raise NotImplementedError("MOs does not have same degree")
+    add_scal = Tree("+", 1, right.coefficient)
+    return Tree("*", add_scal, left)
+
+@add.register(MOMonomial, MOstrPower)
+@special_case(add_filter)
+def momonomial_mostrpower(left, right):
+    """ Add a strpower to a Monomial
+
+    :example:
+    >>> a = MOMonomial(3, "x", 2)
+    >>> b = MOstrPower("x", 2)
+    >>> print(add(a, b))
+    *
+     > +
+     | > 3
+     | > 1
+     > ^
+     | > x
+     | > 2
+    """
+    if left.power != right.power:
+        raise NotImplementedError("MOs does not have same degree")
+    add_scal = Tree("+", left.coefficient, 1)
+    return Tree("*", add_scal, right)
+
+@add.register(MOMonomial, MOMonomial)
+@special_case(add_filter)
+def momonomial_momonomial(left, right):
+    """ Add a Monomial to a Monomial
+
+    :example:
+    >>> a = MOMonomial(3, "x", 2)
+    >>> b = MOMonomial(4, "x", 2)
+    >>> print(add(a, b))
+    *
+     > +
+     | > 3
+     | > 4
+     > ^
+     | > x
+     | > 2
+    """
+    if left.power != right.power:
+        raise NotImplementedError("MOs does not have same degree")
+    add_scal = Tree("+", left.coefficient, right.coefficient)
+    return Tree("*", add_scal, right.strpower)
+
+
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