?? ?????? ??? ???????????? ?????? ??????? ???????? ?????????? ??? ????.The 2 most typical grammatical rules where by this happens is when conjugating previously or existing tenses. For illustrations:???? ????? ???? ???? ???????? ????????????????(??)?? ?????? : ??, ??, ????, ??, ???? ?·???????, ?? ?????? : ?????? ?????????? ??·????????????? ????