User blog comment:Simply Beautiful Art/Fast Array Iteration Leaping/@comment-5529393-20170404001617/@comment-5529393-20170404012838

But, in your reduction rules, you have 1@0, d@0, and d@e always followed by b, which can't be an @ expression because the right hand side has b-1. So you don't have a rule for consecutive @'s.

For F 3 # 5@4 # 1@0 # 2, it looks like you can choose whether to apply the rule for 5@4 or 1@0, unless you mean you always apply the rule for the last @.