∀ {α : Type u} [inst : BEq α] {β : Type v} [EquivBEq α] {k k' : α} {f : Option β → Option β} {l : List ((_ : α) × β)},
  Std.Internal.List.DistinctKeys l →
    Std.Internal.List.containsKey k' (Std.Internal.List.Const.alterKey k f l) =
      if (k == k') = true then (f (Std.Internal.List.getValue? k l)).isSome else Std.Internal.List.containsKey k' l