[1] V. D. BELOUSOV: 
Osnovy teorii kvazigrupp i lap. Izdatel'stvo "Nauka", 1967. 
MR 0218483[2] G. GRÄTZER: 
Universal algebra. D. Van Nostrand, Inc., 1968. 
MR 0248066[3] J. JEŽEK T. KEPKA: 
Free commutative idempotent abelian groupoids and quasigroups. (to appear in Acta Univ. Carolinae). 
MR 0422479[4] J. JEŽEK T. KEPKA: 
The lattice of varieties of commutative abelian distributive groupoids. (to appear in Algebra Universalis). 
MR 0398952[5] J. SOUBLIN: 
Étude algébrique de la notion de moyenne. J. Math. Pures et Appl. 50 (1971), 53-264. 
Zbl 0215.40401