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Lattice theory. Amer. Math. Soc. Colloq. Publ. No. 25, 3rd Edition (Providence, 1967).
MR 0227053 |
Zbl 0153.02501
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[3] LEE SIN-MIN: On a simple one-element extension of countable and finite n-groupoids. (to appear).
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On simple groupoids. Nanta Math. 8 (1975), 30-33.
MR 0417317