1. [1] Ana Castelaz−Commutativity degree of finite groups, A Thesis Submitted to the Graduade Faculty of Wake Forest University, in Partial Fulfillment of the Requirements for the degree of Masters of Arts in the Departament of Mathematics, North Carolina, May (2010).
2. [2] Piergiulio Corsini− Introducere în teoria hipergrupurilor, Ed. Universităt¸ii Alexandru Ioan Cuza, Iaşi, (1998).
3. [3] Piergiulio Corsini, Violeta Leoreanu− Applications of hyperstructures theory, Kluwer Academic Publishers Boston/Dordrechtt/London.
4. [4] Bijan Davvaz− Polygroup Theory and Related Systems, World Scientific Publishing.
5. [5] Paul Erdős, Pál Turán− On Some Problems of a Statistical Group Theory, Acta Mathematica Academiae Scientiarum Hungaricae Tomus 19 (3−4), pp.413 − 435, (1968).10.1007/BF01894517