V. S. Krotkin, O. V. Kuzmin, “On a constructive approach to the calculation of cardinality of the Ryser classes”, Diskr. Mat., 21:3 (2009), 33–36; Discrete Math. Appl., 19:4 (2009), 371–374
Vladislav S. Krotkin, Oleg V. Kuzmin, “Cardinality of the Ryser Classes and the Motzkin Paths with Weights”, J. Sib. Fed. Univ. Math. Phys., 2:3 (2009), 312–318