I obtained a degree of Doctor of Natural Science from University of Science and Technology of China (USTC) in June 2019, and a degree of Doctor of Philosophy from University of Jyvaskyla (JYU) in Finland three months later. Both degrees specilize pure mathematics. My advisors in USTC are Prof. Ping Li and Assoc. Prof. Congwen Liu. Prof. Pekka Koskela is my Finnish supervisor. I have worked in J...