????? ???????? ???????? ??? ????? ???? ?? ????? ???????? ????? ???????. ??? ?????? ??? ??????? ??????? ??? ??????? 12?91 ????? ????? ?? ??? 1999? ???? 86?27 ????? ????? ??????? ????? ?26?63 ????? ????? ??????? ?????.

???? ???????? ???: ????? ??????? ??????? ??????? (1993)? ????? ?????? ??????? ??? ????? ????? ?????? (1999)? ????? ????? ?????? ??????? ????????? ??????? (1999)? ????? ?????? ??????? ??? ??????? ???????? ???????? (1999)? ?????? ????? ??????? ???????? (1999).