1. R. Balbes and G. Grätzer,Injective and projective Stone algebras, Duke Math. J.38 (1971), 339–347.
2. B. Csákány,Characterizations of regular varieties, Acta Sci. Math. (Szeged)31 (1970), 187–189.
3. G. Grätzer,Universal Algebra (Van Nostrand Co., Princeton, N.J., 1968).
4. G. Grätzer,Two Mal’cev-type theorems in universal algebra, J. Comb. Theory8 (1970), 334–342.
5. A. Mal’cev,On the general theory of algebraic systems (Russian), Mat. Sb. N.S. 35,77 (1954), 3–20.