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