8 letter
г к х ш щ ч ц
must be followed by -а/я
can not be followed by -у/ю
7 letter
г к х ш щ ч
must be followed by и
can not be followed by ы
5 letter
ш щ ж ч ц
if о is unstressed it must be followed by е
Hard vs. Soft Stems
Hard
а
э*
о
у
ы
Soft
я
е
ё
ю
и
ь
й
* э: us it part of grammatical russian endings
