Varga Kalantarov, PhD in Math and Professor at Koç University, sent a letter of gratitude to Hamlet Isakhanli. Varga Kalantarov participated in the international conference “Operators, Functions, and Systems of Mathematical Physics” which was held on May 21-24, 2018, on organizational support of the Department of Mathematics of Khazar University, and under the supervisio of International Organization Committee consisting of delegates from Azerbaijan, Russia, Georgia, Turkey, Ukraine, the United States, Sweden and the United Arab Emirates. In the letter, it says: “I came back to Istanbul on the following day of the conference. I am still under the impression of the conference. I share my experience with my close friends. I have contributed to organising of some small meetings on differential equations in Istanbul and Ankara. I can figure out how it is hard to organize a conference which is attended by prominent scholars -A.Aleksandrov, A.Belavin, M. Belishev, A. Helemski, B. Mtyagin, G.Rosenglum and talented younger researchers. Again, I express my gratitude for being invited to the conference of global importance.”