static LS tok_cleanImports(LS tok) {
  LS index = toContentsIndexedList(tok);
  L<IntRange> imports = tok_findImports_returnRanges(tok);
  new BitSet exclude;
  for (IntRange r : imports)
    set(exclude, r.end-4);
    
  new L<IntRange> reToks;
  loop: for (IntRange r : imports) {
    S id = get(tok, r.end-4);
    if (!isIdentifier(id)) continue;
    for (int i : indicesOf(index, id))
      if (!get(exclude, i))
        continue loop; // id is in use
    // import is unused - delete
    clearTokens_addToReToks(tok, r.start+1, r.end, reToks);
  }
  
  reTok_multi(tok, reToks);
  ret tok;
}