Thm_cont.DISJ_CASES

STRUCTURE

SYNOPSIS

Applies separate theorem-tactics to the two disjuncts of a theorem.

DESCRIPTION

If the theorem-tactics f1 and f2, applied to the ASSUMEd left and right disjunct of a theorem |- u \/ v respectively, produce results as follows when applied to a goal (A ?- t):

    A ?- t                                 A ?- t
   =========  f1 (u |- u)      and        =========  f2 (v |- v)
    A ?- t1                                A ?- t2

then applying DISJ_CASES_THEN2 f1 f2 (|- u \/ v) to the goal (A ?- t) produces two subgoals.

           A ?- t
   ======================  DISJ_CASES_THEN2 f1 f2 (|- u \/ v)
    A ?- t1      A ?- t2

FAILURE

Fails if the theorem is not a disjunction. An invalid tactic is produced if the theorem has any hypothesis which is not alpha-convertible to an assumption of the goal.

EXAMPLE

Given the theorem

   th = |- (m = 0) \/ (?n. m = SUC n)

and a goal of the form ?- (PRE m = m) = (m = 0), applying the tactic

   DISJ_CASES_THEN2 SUBST1_TAC ASSUME_TAC th

to the goal will produce two subgoals

   ?n. m = SUC n ?- (PRE m = m) = (m = 0)

   ?- (PRE 0 = 0) = (0 = 0)

The first subgoal has had the disjunct m = 0 used for a substitution, and the second has added the disjunct to the assumption list. Alternatively, applying the tactic

   DISJ_CASES_THEN2 SUBST1_TAC (CHOOSE_THEN SUBST1_TAC) th

to the goal produces the subgoals:

   ?- (PRE(SUC n) = SUC n) = (SUC n = 0)

   ?- (PRE 0 = 0) = (0 = 0)

USES

Building cases tacticals. For example, DISJ_CASES_THEN could be defined by:

  let DISJ_CASES_THEN f = DISJ_CASES_THEN2 f f

SEEALSO

STRIP_THM_THEN, CHOOSE_THEN, CONJUNCTS_THEN, CONJUNCTS_THEN2, DISJ_CASES_THEN, DISJ_CASES_THENL