## In memoriam Petio Petkov

We deeply mourn the death on 26 October 2021 of our long-time colleague and friend

### Dr. Petio Petkov, associate professor (1938-2021).

For us, he will remain an interesting and original researcher in the field of mathematical logic and the foundations of mathematics. Among his colleagues abroad, he is known for his results at the world-famous school of constructive Mathematics, headed by his teacher Professor A. A. Markov. His numerous students will remember his precisely designed lectures on a wide range of mathematical disciplines – from Calculus to Mathematical Logic, Proof Theory and Metamathematics. Students of two generations will remember his textbooks, manuals and books of mathematical problems. In addition to his scientific interests, Petio Petkov showed a renaissance perseverance in discovering and preserving the Bulgarian mathematical heritage. Popularization of mathematical science was an integral part of his life. He successfully used various tribunes–seminars, lectures, colloquiums on logic, historical studios, etc., in order to disseminate the mathematical knowledge to people in all ages, professions and occupations. We ought to mention also his active civic stand in political, trade union and scientific forums. With the death of Petio Petkov, our logical community loses a bright, original and energetic member.

In tribute to his memory! May he rest in peace!

*From the Department of Mathematical logic and its applications at the Faculty of Mathematics and Informatics, Sofia University and the Department of Algebra and Logic at the Institute of Mathematics and Informatics, Bulgarian Academy of Sciences.*