// i = first C token, j = last C token
static LS tok_addCurlyBracketsAroundPart(LS tok, int i, int j) {
  if (i == 1 && j == l(tok)-2) ret tok;
  S pre = get(tok, i-1), post = get(tok, j+1);
  if (endsWith(pre, "{") && startsWith(post, "}"))
    ret tok;
  tokPrepend(tok, i, "{");
  tokAppend(tok, j, "}");
  ret tok;
}