**February 28**

**Zuzana Hanikova**,
Czech Academy of Sciences

**Vopěnka's Alternative Set Theory and its mathematical context**

Vopěnka first presented his Alternative Set Theory (AST) in the monograph 'Mathematics in the Alternative Set Theory' published by Teubner, Leipzig in 1979. Another book presenting the theory, 'Introduction to Mathematics in the Alternative Set Theory', was published in 1989 in Slovak by Alfa, Bratislava. In addition there are numerous journal papers on the AST by members of the research group established by Vopěnka, and the proceedings of a conference dedicated to the AST, also from 1989. In several essays, Vopěnka sought to lay out the motivation and philosophical import of the AST and some of his subsequent work. As one consequence of the emphasis on his philosophy, the mathematical inspiration for the AST has been somewhat obliterated. The aim of the talk is to discuss the design choices Vopěnka made for the AST in relation to pertinent mathematical developments of the 20th century, such as Skolem's work on nonstandard models of arithmetic, Robinson's nonstandard analysis, Rieger's nonstandard models of arithmetic, Vopěnka's nonstandard model of set theory, Vopěnka and Hájek's theory of semisets, or Parikh's almost consistent theories. The presentation will include an outline of the AST following the works of Vopěnka and Sochor. This is a historical talk; no new mathematical results on the AST will be presented.