docs: def contains(self, assertion):
          """
          Returns `True` if `assertion` is contained in this `Independencies`-object,
          otherwise `False`.
  
          Parameters
          ----------
          assertion: IndependenceAssertion()-object
  
          Examples
          --------
          >>> from pgmpy.independencies import Independencies, IndependenceAssertion
          >>> ind = Independencies(['A', 'B', ['C', 'D']])
          >>> IndependenceAssertion('A', 'B', ['C', 'D']) in ind
          True
          >>> # does not depend on variable order:
          >>> IndependenceAssertion('B', 'A', ['D', 'C']) in ind
          True
          >>> # but does not check entailment:
          >>> IndependenceAssertion('X', 'Y', 'Z') in Independencies(['X', 'Y'])
          False
          """
          if not isinstance(assertion, IndependenceAssertion):
              raise TypeError("' in <Independencies()>' requires IndependenceAssertion" +
                              " as left operand, not {0}".format(type(assertion)))
  
          return assertion in self.get_assertions()