\DOC DISCH_TAC
\TYPE {DISCH_TAC : tactic}
\SYNOPSIS
Moves the antecedent of an implicative goal into the assumptions.
\KEYWORDS
tactic, undischarge, antecedent, implication.
\DESCRIBE
{
A ?- u ==> v
============== DISCH_TAC
A u {u} ?- v
}
Note that {DISCH_TAC} treats {~u} as {u ==> F}, so will also work
when applied to a goal with a negated conclusion.
\FAILURE
{DISCH_TAC} will fail for goals which are not implications or negations.
\USES
Solving goals of the form {u ==> v} by rewriting {v} with {u}, although
the use of {DISCH_THEN} is usually more elegant in such cases.
\COMMENTS
If the antecedent already appears in the assumptions, it will be
duplicated.
\SEEALSO
Thm.DISCH, Drule.DISCH_ALL, Thm_cont.DISCH_THEN, Tactic.FILTER_DISCH_TAC,
Thm_cont.FILTER_DISCH_THEN, Drule.NEG_DISCH, Tactic.STRIP_TAC,
Drule.UNDISCH, Drule.UNDISCH_ALL, Tactic.UNDISCH_TAC.
\ENDDOC