∀ {α : Type u} {β : Type v} [inst : Ord α] [Std.TransOrd α] [inst_2 : BEq α] [Std.LawfulBEqOrd α]
  {l : List ((_ : α) × β)},
  Std.Internal.List.DistinctKeys l →
    ∀ {k : α} {f : β → β},
      (Std.Internal.List.Const.modifyKey k f l).isEmpty = false →
        ∀ {fallback : α},
          Std.Internal.List.maxKeyD (Std.Internal.List.Const.modifyKey k f l) fallback =
            if (Std.Internal.List.maxKeyD l fallback == k) = true then k else Std.Internal.List.maxKeyD l fallback