theory Slow
  imports "~~/src/HOL/Number_Theory/Primes"
begin

(* very slow when Primes theory is loaded *)
lemma "((foo::int) + bar * xxx mod 2 ^ 8) mod 2 ^ 8 = baz"
  apply simp
  oops
  
(* this one is faster *)
lemma "((foo::int) + bar * xxx) mod 2 ^ 8 = baz"
  apply simp
  oops
  
end