UNDISCH : (thm -> thm)

SYNOPSIS
Undischarges the antecedent of an implicative theorem.

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  DISCH,   DISCH_ALL,   DISCH_TAC,   DISCH_THEN,   FILTER_DISCH_TAC,   FILTER_DISCH_THEN,   NEG_DISCH,   STRIP_TAC,   UNDISCH_ALL,   UNDISCH_TAC

HOL  Kananaskis 0