let x = 2 + 3
  let w = "4"
  let z = w ^ w
  let y = 2 + x
  let v = z ^ y
  let u = 1.0 + 3.1
  let l1 = [x;y]
  let l2 = l1::l1
  let l3 = 3::l2
  let a = string_of_bool not true
  let b = not a