alias prime {
  var %x $1
  var %y 1
  var %factors 0
  while (%y <= %x) {
    var %fct %x % %y
    if (%fct == 0) { inc %factors }
    inc %y
  }
  if (%factors == 2) {
    msg $active %x is a prime.
  }
  else {
    msg $active %x is not a prime.
  }
}