User blog comment:Hyp cos/R function II/@comment-5529393-20150406080531/@comment-11227630-20150407091610

Read what I just reply Vel!

I made a little change and nR{0+1} is not valid now.

But if there's a number or a brace not separator immediately after it, that's valid.

For example, scan nR{0+1}1. We get A_1 = {0+1}1 and A_2 = {0+1} (i.e. comma) Notice that the A_1 has least level (see section "levels") so it's less than {0}. So we go to step 4.4 and the expression will be nR{0{0+1}1}1. As you see, when we return, the comma now has nested level 2.