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\DOC is_iff
\TYPE {is_iff : term -> bool}
\SYNOPSIS
Tests if a term is an equation between Boolean terms (iff / logical
equivalence).
\DESCRIBE
Recall that in HOL, the Boolean operation variously called logical equivalence,
bi-implication or `if and only if' (iff) is simply the equality relation on
Boolean type. The call {is_iff t} returns {true} if {t} is an equality between
terms of Boolean type, and {false} otherwise.
\FAILURE
Never fails.
\EXAMPLE
{
# is_iff `p = T`;;
val it : bool = true
# is_iff `p <=> q`;;
val it : bool = true
# is_iff `0 = 1`;;
val it : bool = false
}
\SEEALSO
dest_iff, is_eq, mk_iff.
\ENDDOC
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