[1] M. Barr, C. Wells: 
Category Theory for Computing Science. Series in Computer Science, Prentice Hall International, London, 1990. 
MR 1094561[3] W. Bartol, F. Rosselló, L. Rudak: Lectures on Algebras, Equations and Partiality. Rosselló F. (ed.), Technical report B-006, Univ. Illes Balears, Dept. Ciencies Mat. Inf., 1992.
[5] P. Burmeister: 
A Model Theoretic Oriented Approach to Partial Algebras. Math. Research Band 32, Akademie Verlag, Berlin, 1986. 
MR 0854861 | 
Zbl 0598.08004[9] J. Johnson, R. L. Seifer: A survey of multi-unary algebras. Mimeographed seminar notes, U.C. Berkeley, 1967.
[10] B. Jónsson: 
Topics in Universal Algebra. Lecture Notes in Mathemathics 250, Springer-Verlag, 1972. 
MR 0345895[15] K. Pióro: 
On subalgebra lattices of a finite unary algebra, Part II. Math. Bohem. 126 (2001), 171–181. 
MR 1826479