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MR 0152479 |
Zbl 0129.01204
[2] Zelinka В.:
Tolerance in algebraic structures. Czech. Math. J. V, 20 (95), Praha 1970, p. 179-183.
MR 0260653 |
Zbl 0197.01002
[3] Zelinka В.:
Tolerance in algebraic structures II. Czech, Math. J., to appear.
Zbl 0316.08001