User blog comment:Hyp cos/R function II/@comment-5529393-20150406080531/@comment-11227630-20150406084707

The scanning order is not "what you are scanning", but "the position of the thing what you scan". You start scanning from R, or from the lbrace if you just apply case B3 or case C. Case A4 let you scan to the right; case B3 and case C let you scan inside a brace.

For example, scan 2R{0{0+2}01}:

First the brace {0{0+2}01}; then, by case C, scan inside {0{0+2}01}.

Then the 0 immediately before {0+2}; then, by case A4, the 0 immediately before ; then, by case A4, the 1; then, having applied case B3, scan inside .

Then the brace {0,{1}}; then, by case C, scan inside {0,{1}}.

Then the 0 immediately before comma; then, by case A4, the {1}; then, by case C, scan inside {1}.

Then the 1. Now you can apply case B2.