apply Mem.tail
α : Type u_1
n : Nat
x : α
xs : List α
bs : List Bool
pf1 : Nat.succ n < length (x :: xs)
pf2 : Nat.succ n < length (true :: bs)
hnmem : ¬x ∈ xs
hu' : Unique xs
hb : get bs { val := n, isLt := (_ : Nat.succ n ≤ length bs) } = true
⊢ get xs { val := n, isLt := (_ : Nat.succ n ≤ length xs) } ∈ x :: sieve bs xs
case a
α : Type u_1
n : Nat
x : α
xs : List α
bs : List Bool
pf1 : Nat.succ n < length (x :: xs)
pf2 : Nat.succ n < length (true :: bs)
hnmem : ¬x ∈ xs
hu' : Unique xs
hb : get bs { val := n, isLt := (_ : Nat.succ n ≤ length bs) } = true
⊢ Mem (get xs { val := n, isLt := (_ : Nat.succ n ≤ length xs) }) (sieve bs xs)