static L<S> reTok(L<S> tok) {
  replaceCollection(tok, javaTok(tok));
  ret tok;
}

static L<S> reTok(L<S> tok, int i) {
  ret reTok(tok, i, i+1);
}

static L<S> reTok(L<S> tok, int i, int j) {
  // extend i to an "N" token
  // and j to "C" (so j-1 is an "N" token)
  i = i & ~1;
  j = j | 1;
  
  L<S> t = javaTok(join(subList(tok, i, j)));
  replaceListPart(tok, i, j, t);
  
  // fallback to safety
  // reTok(tok);
  
  ret tok;
}