User blog comment:Simply Beautiful Art/Fast Array Iteration Leaping/@comment-5529393-20170404001617

The rules like "F a # ? # .... # ? # 1@0 # b # = F a # ? # .... # ? # 0 # .... # 0 # a # 1@0 # b-1 # .... # c, with a amount of '# 0's" are ambiguous if the ?'s can be 0 or anything with @'s, since you may be able to apply the rule to multiple 1@0's.

Also, the rules require that any c@d is followed by a b, so no two @'s in consecutive terms. It looks like you don't want this.