 The notation of sequents (and, in particular, sequents with only one succedent formula) can, however, be used in a presentation of natural deduction: Gentzen (1936) gives such a system. The notational complications of the different presentations of natural deduction described above—Gentzen’s trees, Jaśkowski’s boxes—are required in order to keep track of just which assumptions a given formula of the proof depends on. An alternative, allowing the use of standard Int-Elim rules, would be to replace each formula in a natural deduction proof with a sequent: the replaced formula standing as the sole succedent formula of the sequent, and the assumptions it depends on forming the antecedent. A system of this sort may be called a system of sequent natural deduction.