Homomorphisms of nets of fixed degree, with singular points on the same line.
(English).Czechoslovak Mathematical Journal,
vol. 26
(1976),
issue 1,
pp. 43,44-54
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[2] V. Havel: To the theory of 4-nets. (Czech); mimeographed in Department of Geometry of the Mathematics Institute of Charles University, Prague 1973, 87 pp.