module fibonacci {

  procedure fib(out int f, obs int n) {
    if(n < 2)
      f = n;
    else
      f = fib(n-1) + fib(n-2);
  }

  procedure fib2(upd int n) {
    if(n < 2)
      ;
    else
      n = fib2(n-1) + fib2(n-2);
  }

  procedure fib3(out int r, obs int n) {
    if(n < 2)
      r = n;
    else {
      var i = 1;
      var j = 0;  // fib(n-2)
      var k = 1;  // fib(n-1)
      var t = 0;
      while(i < n) {
        t = k + j;
	j = k;
	k = t;
	i = i + 1;
      }
      r = t;
    }
  }
        
}