A characterization of Sheffer functions by hyperidentities. Reinhard Pöschel, Klaus Denecke (1988) Semigroup forum

A characterization of the arc by means of the C-index of itssemigroup. K.D. jr. Magill (1993) Semigroup forum

A counting theorem in the semigroup of circulant Boolean matrices Štefan Schwarz (1977) Czechoslovak Mathematical Journal

A half-commutative IP Roth theorem. McCutcheon, R. (2000) Acta Mathematica Universitatis Comenianae. New Series

A matrix characterization of the maximal groups in ${\beta}_{X}$ Darald J. Hartfiel, Carlton J. Maxson (1975) Czechoslovak Mathematical Journal

A maximal chain of principal ideals in the semigroup of binary relations on a finite set. M. Breen (1991) Semigroup forum

A new matrix representation theorem for semigroups. J. Okninski, J.S. Ponizovskii (1996) Semigroup forum

A proof of the Montague-Plemmons-Schein Theorem on maximal subgroups of the semigroup of binary relations. A.H. Clifford (1970) Semigroup forum