diff --git a/chapter04.tex b/chapter04.tex
index 838252e..979e7b8 100644
--- a/chapter04.tex
+++ b/chapter04.tex
@@ -1,6 +1,6 @@
 % -*- coding: utf-8 -*-
 % Translated by Liam0205@bbs.ctex.org
-% Date of translated: 2018-05-09
+% Date of translated: 2018-05-11
 \documentclass{book}
 
 \input{preamble}