ず-stem

〜ざるをえないN2

have no choice but to do; cannot avoid doing

〜ねばならないN2

must do; is obliged to do (written)

〜ぬN3

does not — the classical negative ending

〜ずにすむ

get by without doing; turn out not to have to do

〜ずじまいだN2

ended up never doing; never did get around to doing

〜ずにはいられないN2

cannot help doing; cannot keep oneself from doing

〜ずに〜ず、N3

without doing