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(eng): Triangular norms are, on the one hand, special semigroups and, on the other hand, solutions of some functional equations. This mixture quite often requires new approaches to answer questions about the nature of triangular norms. There are some problems which were stated some time ago and remained unsolved for years. The aim of this paper is to recall some well-known problems of the past and to state several problems which are open and have not been posed so far for a wider audience.