sS unicode_mathBoldScript(S s) {
  new StringBuilder buf;
  for (char c : characters(s)) {
    if (u >= 'a' && u <= 'z')
      buf.append(unicode_mathBoldScript_aToZ_lower(u));
    else if (u >= 'A' && u <= 'Z')
      buf.append(unicode_mathBoldScript_aToZ_upper(u));
    else
      buf.append(c);
  }
  ret str(buf);
}