∀ {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 →
    l.isEmpty = false →
      ∀ {fallback : α}, Std.Internal.List.getKeyD (Std.Internal.List.maxKey! l) l fallback = Std.Internal.List.maxKey! l