(define square (lambda (n) (if (= n 0) 0 (+ (square (- n 1)) (- (+ n n) 1)))))
> (square 4) |(square 4) | (square 3) | |(square 2) | | (square 1) | | |(square 0) | | |0 [Resume previous call, add (2-1)] | | 1 [Resume previous call, add (4-1)] | |4 [Resume previous call, add (6-1)] | 9 [Resume previous call, add (8-1)] |16 [No previous call, so be done] 16 >