STRIP_TAC : tactic

- STRUCTURE
- SYNOPSIS
- Splits a goal by eliminating one outermost connective.
- DESCRIPTION
- Given a goal (A,t), STRIP_TAC removes one outermost occurrence of one of the connectives !, ==>, ~ or /\ from the conclusion of the goal t. If t is a universally quantified term, then STRIP_TAC strips off the quantifier:where x' is a primed variant that does not appear free in the assumptions A. If t is a conjunction, then STRIP_TAC simply splits the conjunction into two subgoals:
A ?- !x.u ============== STRIP_TAC A ?- u[x'/x]

If t is an implication, STRIP_TAC moves the antecedent into the assumptions, stripping conjunctions, disjunctions and existential quantifiers according to the following rules:A ?- v /\ w ================= STRIP_TAC A ?- v A ?- w

where x' is a primed variant of x that does not appear free in A. Finally, a negation ~t is treated as the implication t ==> F.A ?- v1 /\ ... /\ vn ==> v A ?- v1 \/ ... \/ vn ==> v ============================ ================================= A u {v1,...,vn} ?- v A u {v1} ?- v ... A u {vn} ?- v A ?- ?x.w ==> v ==================== A u {w[x'/x]} ?- v

- FAILURE
- STRIP_TAC (A,t) fails if t is not a universally quantified term, an implication, a negation or a conjunction.
- EXAMPLE
- Applying STRIP_TAC twice to the goal:results in the subgoal:
?- !n. m <= n /\ n <= m ==> (m = n)

{n <= m, m <= n} ?- m = n

- USES
- When trying to solve a goal, often the best thing to do first is REPEAT STRIP_TAC to split the goal up into manageable pieces.
- SEEALSO

HOL Kananaskis-14