New statement and proof of free_tv_subst_var in order to cope with new
rewrite rules Un_insert_left, Un_insert_right
(* Title: HOL/RelPow.thy
ID: $Id$
Author: Tobias Nipkow
Copyright 1996 TU Muenchen
R^n = R O ... O R, the n-fold composition of R
*)
RelPow = Nat +
primrec "op ^" nat
"R^0 = id"
"R^(Suc n) = R O (R^n)"
end