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\DOC CCONTR
\TYPE {CCONTR : term -> thm -> thm}
\SYNOPSIS
Implements the classical contradiction rule.
\KEYWORDS
rule, contradiction.
\DESCRIBE
When applied to a term {t} and a theorem {A |- F}, the inference rule {CCONTR}
returns the theorem {A - {{~t}} |- t}.
{
A |- F
--------------- CCONTR `t`
A - {{~t}} |- t
}
\FAILURE
Fails unless the term has type {bool} and the theorem has {F} as its
conclusion.
\COMMENTS
The usual use will be when {~t} exists in the assumption list; in this case,
{CCONTR} corresponds to the classical contradiction rule: if {~t} leads to
a contradiction, then {t} must be true.
\SEEALSO
CONTR, CONTR_TAC, NOT_ELIM.
\ENDDOC
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