∀ {α : Type u} {β : α → Type v} [inst : BEq α] [inst_1 : LawfulBEq α] {l₁ : List ((a : α) × β a)} {l₂ : List α} {k : α},
  Std.Internal.List.DistinctKeys l₁ →
    l₂.contains k = false →
      Std.Internal.List.getValueCast? k (List.filter (fun p => !l₂.contains p.fst) l₁) =
        Std.Internal.List.getValueCast? k l₁