Always_LeadsTo_pre. Always_LeadsTo_post: new equivalences suggested by Misra
(* Title: HOL/ex/natsum.thy
ID: $Id$
Author: Tobias Nipkow
Copyright 1994 TU Muenchen
A summation operator. sum(f,n+1) is the sum of all f(i), i=0...n.
*)
NatSum = Arith +
consts sum :: [nat=>nat, nat] => nat
primrec
"sum f 0 = 0"
"sum f (Suc n) = f(n) + sum f n"
end