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On the semigroup of binary relations on a finite set. Czech. Math. J. 20 (1970), 632-679.
MR 0296190 |
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[3] Schwarz Š.:
On a sharp estimation in the theory of binary relations on a finite set. Czech. Math. J. 20 (1970), 703-714.
MR 0282862 |
Zbl 0226.20061