commit 71585cca3adb5b47b154581144b95947c7e028d2 Author: wangyuhuix Date: Sat Jun 29 23:43:34 2019 +0800 supplement diff --git a/21_supplement.pdf b/21_supplement.pdf new file mode 100644 index 0000000..5dc8d01 Binary files /dev/null and b/21_supplement.pdf differ