SWAP_EXISTS_CONVConv.SWAP_EXISTS_CONV : conv
Interchanges the order of two existentially quantified variables.
When applied to a term argument of the form ?x y. P, the
conversion SWAP_EXISTS_CONV returns the theorem:
|- (?x y. P) = (?y x. P)
SWAP_EXISTS_CONV fails if applied to a term that is not
of the form ?x y. P.