def applyto(self, arg):
        """ self = (\\x.(walk x), (subj -o f))
            arg  = (john        ,  subj)
            returns ((walk john),          f)
        """
        if self.indices & arg.indices: # if the sets are NOT disjoint
            raise linearlogic.LinearLogicApplicationException, "'%s' applied to '%s'.  Indices are not disjoint." % (self, arg)
        else: # if the sets ARE disjoint
            return_indices = (self.indices | arg.indices)

        try:
            return_glue = linearlogic.ApplicationExpression(self.glue, arg.glue, arg.indices)
        except linearlogic.LinearLogicApplicationException:
            raise linearlogic.LinearLogicApplicationException, "'%s' applied to '%s'" % (self.simplify(), arg.simplify())

        arg_meaning_abstracted = arg.meaning
        if return_indices:
            for dep in self.glue.simplify().antecedent.dependencies[::-1]: # if self.glue is (A -o B), dep is in A.dependencies
                arg_meaning_abstracted = self.make_LambdaExpression(logic.Variable('v%s' % dep), 
                                                                    arg_meaning_abstracted)
        return_meaning = self.meaning.applyto(arg_meaning_abstracted)

        return self.__class__(return_meaning, return_glue, return_indices)