return c >= 0x0041 && c <= 0x005A ||
        c >= 0x0061 && c <= 0x007A ||
        c >= 0x00C0 && c <= 0x00D6 ||
        c >= 0x00D8 && c <= 0x00F6 ||
        c >= 0x00F8 && c <= 0x00FF ||