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is_imp                                                    (boolSyntax)
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is_imp : term -> bool

SYNOPSIS
Tests a term to see if it is an implication or a negation.

DESCRIBE
If {M} has the form {t1 ==> t2}, or the form {~t}, then {is_imp M}
returns {true}. If the term is neither an implication nor a negation
the result is {false}.

FAILURE
Never fails.

COMMENTS
Yields true of negations because {dest_imp} destructs negations (for
backwards compatibility with PPLAMBDA). Use {is_imp_only} if you don’t want
this behaviour.

SEEALSO
boolSyntax.mk_imp, boolSyntax.dest_imp, boolSyntax.is_imp_only,
boolSyntax.dest_imp_only.

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