Rasykh Farukovich Salakhov,
Kazan Federal University,
18 Kremlyovskaya Str., Kazan, 420008, Russian Federation,
rasih@mail.ru.
Elena Vladimirovna Gabdrakhmanova,
Kazan Federal University,
18 Kremlyovskaya Str., Kazan, 420008, Russian Federation,
akyla66@inbox.ru.