(f2 5)                |       f2(5)
 (f2i 1   1)           |       f2i(5,   1, 1)
 (f2i 1   2)           |       f2i(5,   1, 2)
 (f2i 2   3)           |       f2i(5,   2, 3)
 (f2i 6   4)           |       f2i(5,   6, 4)
 (f2i 24  5)           |       f2i(5,  24, 5)
 (f2i 120 6)           |       f2i(5, 120, 6)
 120                   |       120
                       |       120
                       |       120
                       |       120
                       |       120
                       |       120
                       |       120
      (SCHEME/LISP)    |            (C/C++)