static bool isSingleQuoteIdentifier(S s) {
  if (l(s) < 2 || s.charAt(0) != '\'' || !Character.isJavaIdentifierStart(s.charAt(1))) false;
  for (int i = 2; i < l(s); i++)
    if (!Character.isJavaIdentifierPart(s.charAt(i))) false;
  true;
}