File: IMP_ELIM.doc

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\DOC IMP_ELIM

\TYPE {IMP_ELIM : (thm -> thm)}

\SYNOPSIS
Transforms {|- s ==> t} into {|- ~s \/ t}.

\KEYWORDS
rule, implication, disjunction, negation.

\DESCRIBE
When applied to a theorem {A |- s ==> t}, the inference rule {IMP_ELIM}
returns the theorem {A |- ~s \/ t}.
{
    A |- s ==> t
   --------------  IMP_ELIM
    A |- ~s \/ t
}
\FAILURE
Fails unless the theorem is implicative.

\SEEALSO
NOT_INTRO, NOT_ELIM.

\ENDDOC