\DOC UNDISCH
\TYPE {UNDISCH : (thm -> thm)}
\SYNOPSIS
Undischarges the antecedent of an implicative theorem.
\KEYWORDS
rule, undischarge, antecedent.
\DESCRIBE
{
A |- t1 ==> t2
---------------- UNDISCH
A, t1 |- t2
}
Note that {UNDISCH} treats {"~u"} as {"u ==> F"}.
\FAILURE
{UNDISCH} will fail on theorems which are not implications or negations.
\COMMENTS
If the antecedent already appears in the hypotheses, it will not be
duplicated.
However, unlike {DISCH},
if the antecedent is alpha-equivalent to one of the hypotheses,
it will still be added to the hypotheses.
\SEEALSO
Thm.DISCH, Drule.DISCH_ALL, Tactic.DISCH_TAC, Thm_cont.DISCH_THEN,
Tactic.FILTER_DISCH_TAC, Thm_cont.FILTER_DISCH_THEN, Drule.NEG_DISCH,
Tactic.STRIP_TAC, Drule.UNDISCH_ALL, Tactic.UNDISCH_TAC.
\ENDDOC