strip_exists
boolSyntax.strip_exists : term -> term list * term
Iteratively breaks apart existential quantifications.
If M has the structure ?x1 ... xn. t then strip_exists M returns
([x1,...,xn],t). Note that
strip_exists(list_mk_exists(["x1";...;"xn"],"t"))
will not return ([x1,...,xn],t) if t is an existential
quantification.
Failure
Never fails.