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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _propagate_incompatibility( self, incompatibility ):
 # type: (Incompatibility) -> Union[str, _conflict, None] """ If incompatibility is almost satisfied by _solution, adds the negation of the unsatisfied term to _solution. If incompatibility is satisfied by _solution, returns _conflict. If incompatibility is almost satisfied by _solution, returns the unsatisfied term's package name. Otherwise, returns None. """

        # The first entry in incompatibility.terms that's not yet satisfied by
        # _solution, if one exists. If we find more than one, _solution is
        # inconclusive for incompatibility and we can't deduce anything.
        unsatisfied = None

        for term in incompatibility.terms:
            relation = self._solution.relation(term)

            if relation == SetRelation.DISJOINT:
                # If term is already contradicted by _solution, then
                # incompatibility is contradicted as well and there's nothing new we
                # can deduce from it.
                return
            elif relation == SetRelation.OVERLAPPING:
                # If more than one term is inconclusive, we can't deduce anything about
                # incompatibility.
                if unsatisfied is not None:
                    return

                # If exactly one term in incompatibility is inconclusive, then it's
                # almost satisfied and [term] is the unsatisfied term. We can add the
                # inverse of the term to _solution.
                unsatisfied = term

        # If *all* terms in incompatibility are satisfied by _solution, then
        # incompatibility is satisfied and we have a conflict.
        if unsatisfied is None:
            return _conflict

        self._log(
            "derived: {}{}".format(
                "not " if unsatisfied.is_positive() else "", unsatisfied.dependency
            )
        )

        self._solution.derive(
            unsatisfied.dependency, not unsatisfied.is_positive(), incompatibility
        )

        return unsatisfied.dependency.name