, 2015, The validity of moral rules and principles as a legal problem, in M. Araszkiewicz, P. Banaś, T. Gizbert-Studnicki & K. Płeszka (eds.), Problems of normativity, rules and rule-following, Dordrecht, Springer, pp. 341-349.
, 2013a, Juristic concept of the validity of statutory law: a critique of contemporary legal nonpositivism, Springer, Dordrecht.