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No one shall drive us out of the paradise that Cantor has created with the set theory.
D. Hilbert

Set theory

Z.Janiszewski (1918):
On the needs of mathematics in Poland
... Polish mathematicians do not have to be satisfied with the role of followers and customers of foreign mathematical centres but can achieve an independent position for Polish mathematics. One of the best ways of achieving this goal was for groups of mathematicians to concentrate on relatively narrow fields in which Polish mathematicians had common interests and - more importantly - had already made internationally important contributions. These areas included set theory, and the foundations of mathematics.