Lin Qun, an academician of Chinese Academy of Sciences, gave an interesting first lesson to the freshmen of Grade 2019 at School of Mathematics, Tianjin University on the afternoon of September 5, 2019. As a part-time professor in Tianjin University in the 1980s, Academician Lin Qun said he was very happy to return to Tianjin University again. He discussed the fun of learning mathematics, showing how to learn calculus for the freshmen with plain language and vivid examples on the lecture.

Academician Lin Qun is a famous mathematician in the field of functional analysis and computational mathematics in China who devotes himself to the popularization of calculus. In the lecture, academician Lin pointed out that we should not only recite formulas, memorize theorems and verify proofs, but also understand and innovate when studying mathematics. Academician Lin explained with examples around him that it would be difficult to go a long way in mathematics research if one only recited and applied theorems.

Academician Lin believed that there are many directions and branches in mathematics research and not all of them could be explored, so it was very important to choose the right direction. With right direction and timeless effort, we would succeed sooner or later.

At the same time, he told students that minimalism would also be advocated to grasp main contradictions. Calculus and basic theorems should be well-learned. However, many definitions were very complicated in classical textbooks. For example, in calculus, “ε-δ” language and infinitesimal, are not easy for students to understand. If we only studied elementary functions we often used, differential could be described by simple linear inequalities while integral was to find area, so the basic theorem of calculus, Newton Leibniz formula which is to convert the area of the pancake into the length of the stick became simple and easy to understand.

In the interactive communication, the students consulted academician Lin about problems and puzzles in mathematics learning. He all responded wittily, and drew on Dean Sun to answer together from time to time. Dean Sun called on students to learn from Academician Lin how to maintain interest in mathematics, to explore how to use simple methodologies, and to find sense of fun and achievement in innovation.

Academician Lin Qun, who is 84 years old, showed his innocence in the lecture, walking back and forth from time to time, and answering questions with humour. Perhaps it is the motive force for mathematicians to climb to the top of mathematics that they can always maintain their innocence. Students in School of Mathematics are standing in front of the door of Mathematics, ready to have a try.