CONTRAPOS : (thm -> thm)

SYNOPSIS
Deduces the contrapositive of an implication.

DESCRIBE
When applied to a theorem A |- s ==> t, the inference rule CONTRAPOS returns its contrapositive, A |- ~t ==> ~s.
     A |- s ==> t
   ----------------  CONTRAPOS
    A |- ~t ==> ~s

FAILURE
Fails unless the theorem is an implication.

SEEALSO  CCONTR,   CONTR,   CONTRAPOS_CONV,   NOT_ELIM

HOL  Kananaskis 0