to operate :a :b
  (print [a =] :a)
  (print [b =] :b)
  (print [a + b =] :a + :b)
  (print [a - b =] :a - :b)
  (print [a * b =] :a * :b)
  (print [a / b =] int :a / :b)
  (print [a mod b =] modulo :a :b)
end