The Mathematical Society, which was founded in 1965 by Lê Văn Thiêm (I was general secretary), organized joint seminars in optimization, probability, functional analysis, algebra, numerical analysis. People from Hanoi University, the Pedagogical Institute, and the Polytechnic Institute participated (the Hanoi Mathematical Institute was not formed until 1970). Since the three institutions had been evacuated in different directions from Hanoi, we held the seminars in Hanoi. They met twice a month. I must say, people were very diligent about attending. Many of us would take advantage of the opportunity to visit our families. Since my wife and children were on the opposite side of Hanoi from the university, it was much more convenient for me to visit them after the seminars held in Hanoi.

... he visited in November 1967. The first few days we organized his lectures in Hanoi. But one day a missile exploded only 100-200 meters from the lecture hall. As a result the higher education minister $Tạ Quang Bửu$ ordered us to be evacuated. I remember that Grothendieck was delighted with the news that we were being evacuated, and approached the unusual situation in a spirit of adventure. He gave a "short course" in category theory, homological algebra, and algebraic geometry, with $Đoàn Quỳnh$ as the main translator from French into Vietnamese. Grothendieck would lecture for four hours in the morning, and then hold consultations all afternoon. Even so, he always complained that he was underemployed. He was a strict vegetarian and observed a fast day every Monday.