User blog comment:Wythagoras/Dollar function: final version/@comment-5529393-20131116082407/@comment-5529393-20131118055833

But wait, rule 6 just says:

"If the active bracket has level k, search for the least nested bracket with level (k-1) with the same array in it."

That's all it says. It doesn't say to actually do anything. So I don't see why a$0]2] = a$[[[...].

Also, subrule 2 doesn't say _where_ to add bracket k-1.