[1] K. K. Hang Butler, J. R. Krabill: Circulant Boolean relation matrices. Czech. Math. J. 24 (1974), 247-251. MR 0348017

[2] Št. Schwarz: On the semigroup of binary relations on a finite set. Czech. Math. J. 20 (1970), MR 0296190 | Zbl 0228.20034