EXISTS_TAC

Tactic.EXISTS_TAC : (term -> tactic)

Reduces existentially quantified goal to one involving a specific witness.

When applied to a term u and a goal ?x. t, the tactic EXISTS_TAC reduces the goal to t[u/x] (substituting u for all free instances of x in t, with variable renaming if necessary to avoid free variable capture).

    A ?- ?x. t
   =============  EXISTS_TAC "u"
    A ?- t[u/x]

Failure

Fails unless the goal’s conclusion is existentially quantified and the term supplied has the same type as the quantified variable in the goal.

Example

The goal:

   ?- ?x. x=T

can be solved by:

   EXISTS_TAC ``T`` THEN REFL_TAC

See also

Thm.EXISTS