: arithmetic ( ab- )
  over    "\na       = %d" puts
  dup     "\nb       = %d" puts
  2over + "\na + b   = %d" puts
  2over - "\na - b   = %d" puts
  2over * "\na * b   = %d" puts
  /mod    "\na / b   = %d" puts
          "\na mod b = %d\n" puts ;
