User blog comment:Hyp cos/R function II/@comment-2033667-20150408182105

If we try evaluating nR{0+1}0, then we scan to the first 0 and case A3 applies. We set S1 to the string "{0+1}". s = 1 so we set t := 1. We enter the loop and decrement to t := 0. However there is no way to choose S0, since there is no brace outside of S1. Furthermore, even if there was such an S, t will just keep being decremented infinitely.