User blog comment:Simply Beautiful Art/Fast Array Iteration Leaping/@comment-5529393-20170403230715/@comment-31663462-20170404000351

Notice the line above F a = a + 1 we have ?,d = 0 or anything involving @'s, thus the second rule says to remove the last argument if it is zero or involving @'s (and no #'s). Also, thanks for pointing out the second point, fixed it.