code: public static int indexOf(CharSequence seq, CharSequence pattern, int fromIndex)
      {
          return indexOf(seq, pattern, (int a, int b)->{return a==b;}, fromIndex);
      }
docs: Returns index of pattern, starting at fromIndex, or -1 if pattern not found
  @param seq
  @param pattern
  @param fromIndex
  @return
  @see java.lang.String#indexOf(java.lang.String, int)