∀ {α : Type u} {β : α → Type v} [inst : Ord α] [Std.TransOrd α] [inst_2 : BEq α] [Std.LawfulBEqOrd α]
  [inst_4 : Inhabited α] {l : List ((a : α) × β a)},
  Std.Internal.List.DistinctKeys l →
    ∀ {he : Std.Internal.List.containsKey (Std.Internal.List.maxKey! l) l = true},
      Std.Internal.List.getKey (Std.Internal.List.maxKey! l) l he = Std.Internal.List.maxKey l ⋯