md5_hash("hello_world",12,"0f723ae7f9bf07744445e93ac5595156").
md5_valid("hello_world",12,"0f723ae7f9bf07744445e93ac5595156",X) :-
  md5_check("hello",6,"b1946ac92492d2347c6235b4d2611184",X),
  md5_check("world",6,"591785b794601e212b260e25925636fd",X).