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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 reduce_by(self, package_request):
 """Remove variants whos dependencies conflict with the given package request. Returns: (VariantSlice, [Reduction]) tuple, where slice may be None if all variants were reduced. """

        if self.pr:
            reqstr = _short_req_str(package_request)
            self.pr.passive("reducing %s wrt %s...", self, reqstr)

        if self.solver.optimised:
            if package_request in self.been_reduced_by:
                return (self, [])

        if (package_request.range is None) or \
                (package_request.name not in self.fam_requires):
            return (self, [])

        with self.solver.timed(self.solver.reduction_time):
            return self._reduce_by(package_request)