src/ZF/Let.ML

new lemmas for closure under Union

(*  Title:      ZF/Let
    ID:         $Id$
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1995  University of Cambridge

Let expressions -- borrowed from HOL
*)

val [prem] = goalw (the_context ())
    [Let_def] "(!!x. x=t ==> P(u(x))) ==> P(let x=t in u(x))";
by (rtac (refl RS prem) 1);
qed "LetI";