Romanization of Bulgarian
The system is not invertible, for А, Ж, Й, Ц, Ш, Щ, Ю, Я are transliterated in the same way as are Ъ, ЗХ, Ь, ТС, СХ, ШТ, ЙУ, ЙА respectively.  An auxiliary, invertible variant of the system without the ИЯ-exception rule is proposed by L. Ivanov, D. Skordev and D. Dobrev to be used in those special cases when the exact retrieval of Bulgarian words from their Romanized forms is a priority, with Cyrillic letters and combinations of letters