Incidentally, in recent years, he was affiliated with the regional university here in Pilsen but I never met him here; he mostly used the affiliation to write some mostly historical books, and he wrote many books.

As Google Scholar tells you, he wrote some papers that were famous, relatively to what was usual in Czechoslovakia.

He was born in 1935 in a village in Central Bohemia and like your humble correspondent, he has studied the [then newly founded] Faculty of Mathematics and Physics (MFF) at the Charles University (UK) in Prague. When he was writing his diploma thesis, he was the last student of Eduard Čech, a mathematician whom many (Czech and international) readers know thanks to the Čech cohomology (yes, you may check and bet a cheque that Čech means Czech in Czech and Čech was Czech, too LOL).

In 1968, he was supposed to become a full professor but after the Warsaw Pact occupation, he was seen as politically inconvenient so this promotion only took place in 1990, after the Velvet Revolution.

He surely deserved it. His most famous contributions are linked to the so-called alternative set theory where all sets are formally finite and axioms for them are equivalent to those in Zermelo-Fraenkel set theory; but they allow subclasses which are not sets. Correct me if I am wrong but I see it as a sort of hybrid of ZF and Gödel-Bernays axiom systems.

About 1/2 of what I have ever known about set theory was taught to me by Prof Vopěnka.

*Faculty of Mathematics and Physics at the Lesser Town Square (on the picture: under the net)*

I came to the Charles University in Fall 1992. The math-phys faculty (MFF UK) has 4 major buildings in Prague: Karlov (3-5 Ke Karlovu St), Karlín (Sokolovská 83), Trója (V Holešovičkách 2), and Lesser Town (Malostranské náměstí 25).

Those of us who were not from Prague lived at the Trója student hostels which are close to the "modern socialist" physics buildings of MFF UK – shared with the nuclear faculty of the Czech Technical University – where most of the physicists' courses took place.

However, we also had some courses (like Calculus, Linear Algebra, and Experimental Labs) in Karlov, the original "moderately historical" building where MFF UK was established – many "traditional" experimental physicists work there and basic math courses are taught there. And sometimes we went to Karlín, an "older socialist" building, where most of the mathematicians (analysis, statistics etc.) are employed.

The Lesser Town building is clearly the most historically impressive one. The math-phys building is literally connected to the rather famous Church of St Nicholas (with the thin plus fat church tower). Recall that the Prague Castle is above and not far from the Lesser Town. The MFF UK part of the Lesser Town Square building was nicely renovated in recent years. And that's the building where Vopěnka, other set theorists, mathematical logicians, as well most computer scientists and mathematical linguists etc. are located.

A physics student normally

*never*goes to that building but my roommate and friend JS (who was also a physics student, and later subnuclear physicist) convinced me to attend Vopěnka's lectures, and I was happy that he did.

Aside from set theory, we were told lots of wonderful stories about Vopěnka's political experience. Right after the Velvet Revolution, between 1990 and 1992, he was the Czech minister of education (these "cultural" ministries were divided between Czechia and Slovakia even before Czechoslovakia was dissolved).

For example, I remember his funny story about the Azerbaijani ambassadors who were used to visit the ministry of education and get some fancy alcoholic beverages. Vopěnka hosted them with mineral water. Of course that they didn't show up again.

Vopěnka was a rare minister of education – unlike his 7 or so predecessors, he wasn't mentally ill. One famous minister of education believed in paranormal phenomena and did research into them, and so on, and so on.

There is one more thing that Vopěnka should be credited for, in my opinion. As far as I know, he was the very first top-level Czech politician who actually began to defend the separation of Czechoslovakia. He was convinced it was the right thing to do already well before the mid 1992 elections (which made the dissolution since January 1st, 1993 unavoidable).

His arguments were not terribly surprising – it's not a great idea to subsidize Slovakia; it's intriguing to get rid of some of the unrefined old-fashioned nationalism that was loud in Slovakia; and so on, and so on – but he could see that the dissolution was doable at the moment.

That was rare because people would love to say that the dissolution of Czechoslovakia would mean a catastrophe, perhaps a civil war, and so on, and so on. You know, no such dissolution was ever done smoothly before us – and after us, for that matter. Almost all Czech politicians (and the Czech cultural front, not to mention most of the Czech population) were vocally defending the preservation of Czechoslovakia almost at any price – up to the 1992 elections (while in Slovakia, the open separatism and various pro-confederacy mixed ideas were much more widespread since late 1989) but Vopěnka knew better and was in some sense (and I surely don't mean an offending sense) the "mirror image" of the separatist attitudes in Slovakia.

Of course, the motivation and good work of others were needed for the dissolution to

*actually*be smooth and peaceful. But I do think that in those respects, he was ahead of others.

RIP, Prof Vopěnka.

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