Breaks an implication or negation into antecedent and consequent.
DESCRIPTION
dest_imp is a term destructor for implications. It treats negations as
implications with consequent F. Thus, if M is a term with the form
t1 ==> t2, then dest_imp M returns (t1,t2), and if M has the
form ~t, then dest_imp M returns (t,F).
FAILURE
Fails if M is neither an implication nor a negation.
COMMENTS
Destructs negations for increased functionality of HOL-style resolution.
If the ability to destruct negations is not desired, as is only right,
then use dest_imp_only.