Článek je vzpomínkou na Jaroslava Foltu CSc. Byl to přední český odborník na historii matematiky, její propagátor a popularizátor. Po dlouhé a těžké nemoci zemřel 25. března 2011 ve věku 78 let. Článek poskytuje jeho stručný životopis, kde je popsán jeho přínos matematické obci a nabízí webové stránky, kde je jeho životopis vypsán podrobně.
Bz the quadrileteral condition in a given net there is meant the following implication: If are arbitrary points, no three of them lie on the same line, with coll (collinearity) for any five from six couples then there follows the collinearity coll for the remaining couple . In the article there is proved the every net satisfying the preceding configuration condition is necessarity the Ostrom net (i.e., the net over a field). Conversely, every Ostrom net satisfies the above configuration...
When mathematical models describing various processes are analysed, the fact of existence of a positive solution is often among the basic features. In this paper, a general delayed discrete equation is considered. Sufficient conditions concerning are formulated in order to guarantee the existence of a positive solution for . An upper estimate for it is given as well. The appearance of the positive solution takes its origin in the nature of the equation considered since the results hold only...
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