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Date: Tue, 15 Jun 93 15:44:07 -0700
From: toal@cs.ucla.edu (Ray Toal)
Message-Id: <9306152244.AA05095@maui.cs.ucla.edu>
To: info-hol@ted.cs.uidaho.edu, slind@informatik.tu-muenchen.de, 
    toal@cs.ucla.edu
Subject: Re: A simple question

From Konrad Slind's EXISTS_NTH_TAC example it is easy to obtain


letrec SIFT_EXISTS_CONV x t =
  let bvars = fst (strip_exists t) in
  if not (mem x bvars) then failwith `Variable not bound`
  else if x = hd bvars then ALL_CONV t
  else if x = hd (tl bvars) then SWAP_EXISTS_CONV t
  else (RAND_CONV (ABS_CONV (SIFT_EXISTS_CONV x)) THENC SWAP_EXISTS_CONV) t;;

let MY_EXISTS_TAC x u =
  CONV_TAC (SIFT_EXISTS_CONV x) THEN
  EXISTS_TAC u;;

Ray