constructor
α : Type u_1
da : DecidableEq α
x y : α
ys : List α
h : DifferentList (x :: y :: ys)
⊢ (y != x) = true ∧ List.foldr (fun a r => a != x && r) true ys = true
case left
α : Type u_1
da : DecidableEq α
x y : α
ys : List α
h : DifferentList (x :: y :: ys)
⊢ (y != x) = true

case right
α : Type u_1
da : DecidableEq α
x y : α
ys : List α
h : DifferentList (x :: y :: ys)
⊢ List.foldr (fun a r => a != x && r) true ys = true