fix import and bug but div for absPoly

pymath/calculus/__init__.py

@@ -4,6 +4,7 @@
 from .expression import Expression
 from .polynom import Polynom
 from .fraction import Fraction
+from .equation import Equation
 from .random_expression import random_str
 from .render import txt
 

pymath/calculus/abstract_polynom.py

@@ -675,7 +675,7 @@ class AbstractPolynom(Explicable):
         ans = AbstractPolynom(ans_coefs, letter=self._letter)
         ini_step = [Step(
             self.postfix_tokens +
-            [other, op.mul]
+            [other, op.div]
             )]
 
         ans = ans.simplify()