sad news, apologies if you already know this

[Kreinovich, Vladik]

Gregory Tseytin, one of the founding fathers of what is now called Russian Constructivism, died on August 27. He independently proved in the 1950s that every constructive function is constructively continuous, and proved many other results, Kushner’s book Lectures on Constructive Mathematical Analysis has a lot of references to his results.

[Toby Bartels]

Very sad to hear this!

Readers might recognize his name as Ceitin; at any rate, I always see references to Ceitin's Theorem. And his work on combinatorial logic was published as Tseitin. (These are all different ways to Romanize the original Russian Цейтин.)

—Toby Bartels