DISJ_CASES_THEN : thm_tactical
STRUCTURE
Thm_cont
SYNOPSIS
Applies a theorem-tactic to each disjunct of a disjunctive theorem.
DESCRIPTION
If the theorem-tactic f:thm->tactic applied to either ASSUMEd disjunct produces results as follows when applied to a goal (A ?- t): 
    A ?- t                                A ?- t
   =========  f (u |- u)      and        =========  f (v |- v)
    A ?- t1                               A ?- t2
then applying DISJ_CASES_THEN f (|- u \/ v) to the goal (A ?- t) produces two subgoals. 
           A ?- t
   ======================  DISJ_CASES_THEN f (|- 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_THEN ASSUME_TAC th
produces two subgoals, each with one disjunct as an added assumption: 
   ?n. m = SUC n ?- (PRE m = m) = (m = 0)

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

USES
Building cases tactics. For example, DISJ_CASES_TAC could be defined by: 
   val DISJ_CASES_TAC = DISJ_CASES_THEN ASSUME_TAC

COMMENTS
Use DISJ_CASES_THEN2 to apply different tactic generating functions to each case.
SEEALSO
CHOOSE_THEN, CONJUNCTS_THEN, CONJUNCTS_THEN2, DISJ_CASES, DISJ_CASES_TAC, DISJ_CASES_THEN2, DISJ_CASES_THENL, STRIP_THM_THEN
HOL  Kananaskis-14