EXISTS_TAC : (term -> tactic)
STRUCTURE
SYNOPSIS
Reduces existentially quantified goal to one involving a specific witness.
DESCRIPTION
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
SEEALSO
HOL  Kananaskis-14