File: CONTRAPOS_CONV.doc

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\DOC CONTRAPOS_CONV

\TYPE {CONTRAPOS_CONV : conv}

\SYNOPSIS
Proves the equivalence of an implication and its contrapositive.

\KEYWORDS
conversion, contrapositive, implication.

\DESCRIBE
When applied to an implication {P ==> Q}, the conversion {CONTRAPOS_CONV}
returns the theorem:
{
   |- (P ==> Q) = (~Q ==> ~P)
}
\FAILURE
Fails if applied to a term that is not an implication.

\SEEALSO
CONTRAPOS.

\ENDDOC