|
<center>''' 丁剑 '''<br><img src=" https://www.math.pku.edu.cn/images/content/2021-12/20211231160316366170.jpg " width="180"></center><small>[ https://www.math.pku.edu.cn/jsdw/js_20180628175159671361/d_20180628175159671361/134395.htm 北京大学数学学院]
</small>