Added some sums.
(* 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"
rules sum_0 "sum(f,0) = 0"
sum_Suc "sum(f,Suc(n)) = f(n) + sum(f,n)"
end