intros h
α : Type u_1
da : DecidableEq α
x : α
xs : List α
⊢ DifferentList (x :: xs) → (List.all xs fun x_1 => x_1 != x) = true
α : Type u_1
da : DecidableEq α
x : α
xs : List α
h : DifferentList (x :: xs)
⊢ (List.all xs fun x_1 => x_1 != x) = true