list_mk_exists
boolSyntax.list_mk_exists : term list * term -> term
Iteratively constructs an existential quantification.
list_mk_exists([x1,...,xn],t) returns ?x1 ... xn. t.
Failure
Fails if the terms in the list are not variables or if t is not of
type bool and the list of terms is non-empty. If the list of terms is
empty the type of t can be anything.