DISJ_CASES_TAC : thm_tactic

SYNOPSIS
Produces a case split based on a disjunctive theorem.

DESCRIBE
Given a theorem th of the form A |- u \/ v, DISJ_CASES_TAC th applied to a goal produces two subgoals, one with u as an assumption and one with v:
              A ?- t
   ============================  DISJ_CASES_TAC (A |- u \/ v)
    A u {u} ?- t   A u {v}?- t

FAILURE
Fails if the given theorem does not have a disjunctive conclusion.

EXAMPLE
Given the simple fact about arithmetic th, |- (m = 0) \/ (?n. m = SUC n), the tactic DISJ_CASES_TAC th can be used to produce a case split:
   - DISJ_CASES_TAC th ([],Term`(P:num -> bool) m`);
   ([([`m = 0`], `P m`),
     ([`?n. m = SUC n`], `P m`)], fn) : tactic_result

USES
Performing a case analysis according to a disjunctive theorem.

SEEALSO  ASSUME_TAC,   ASM_CASES_TAC,   COND_CASES_TAC,   DISJ_CASES_THEN,   STRUCT_CASES_TAC

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