User blog comment:Hyp cos/R function II/@comment-5529393-20150406080531

So, I'm trying to evaluate something simple like 3R{{0,2},2}. First you scan to the 0, and by rule A4 you keep scanning. Next comes the comma, which is equivalent to {0 +1}. So we go to case A3. We have s=1. We go to step 2, which sets t=1, then we decrement t to 0 in step 2.1. We have S_1 = {0 +1}, so we will set S_0 = {0 {0 +1} 2}, and S_{-1} to {{0 {0 +1} 2} {0 +1} 2}, and then we run into a problem when we try to set S_{-2}.

So, let's say step 2 is skipped when t=1 to start. In step 3, we set k = m = 1, and s(1) = s = 1. In step 4 we decrement k to 0, then set s(0) = s(1) = 1. In step 4.3, we decrement s(0) to 0, then "If level A_s(0) < level A_s(1)", but A_s(0) = A_0 hasn't been defined, only A_1 so far.

So, I'm having trouble evaluating your notation.