INDUCT_TAC reduces a goal !n.P[n], where n has type num, to two
subgoals corresponding to the base and step cases in a proof by mathematical
induction on n. The induction hypothesis appears among the assumptions of the
subgoal for the step case.  The specification of INDUCT_TAC is:
                A ?- !n. P
    ========================================  INDUCT_TAC
     A ?- P[0/n]     A u {P} ?- P[SUC n'/n]