English
The kernel of a homomorphism to a domain is a prime ideal.
Русский
Ядро гомоморфизма векторного кольца к области является простым идеалом.
LaTeX
$$$(\\ker f).IsPrime$$
Lean4
/-- The kernel of a homomorphism to a domain is a prime ideal. -/
theorem ker_isPrime {F : Type*} [Semiring R] [Semiring S] [IsDomain S] [FunLike F R S] [RingHomClass F R S] (f : F) :
(ker f).IsPrime :=
have := Ideal.bot_prime (α := S)
inferInstanceAs (Ideal.comap f ⊥).IsPrime