\DOC FILTER_GEN_TAC
\TYPE {FILTER_GEN_TAC : (term -> tactic)}
\SYNOPSIS
Strips off a universal quantifier, but fails for a given quantified
variable.
\KEYWORDS
tactic, selective, quantifier, universal.
\DESCRIBE
When applied to a term {s} and a goal {A ?- !x. t}, the tactic
{FILTER_GEN_TAC}
fails if the quantified variable {x} is the same as {s}, but otherwise
advances the goal in the same way as {GEN_TAC}, i.e. returns the goal
{A ?- t[x'/x]} where {x'} is a variant of {x} chosen to avoid clashing
with
any variables free in the goal's assumption list. Normally {x'} is just
{x}.
{
A ?- !x. t
============== FILTER_GEN_TAC "s"
A ?- t[x'/x]
}
\FAILURE
Fails if the goal's conclusion is not universally quantified or the
quantified variable is equal to the given term.
\SEEALSO
Thm.GEN, Tactic.GEN_TAC, Drule.GENL, Drule.GEN_ALL, Thm.SPEC,
Drule.SPECL, Drule.SPEC_ALL, Tactic.SPEC_TAC, Tactic.STRIP_TAC.
\ENDDOC