diff --git a/.gitignore b/.gitignore
index 722f6ea..a2f60c6 100755
--- a/.gitignore
+++ b/.gitignore
@@ -1,24 +1,13 @@
 # .gitignore
 
-src/img.rb
-src/imgsize.rb
-src/toi.rb
-src/misc/cairo2.c
-src/misc/cairo2.pdf
-src/misc/color_square.c
-src/misc/color_square.png
-src/tfe/hello.txt
-src/tfe/resources.c
-src/tfe5/hello.txt
-src/temp
-src/le
-latex/*
+# temporary directory
+src/temp/
 
 # build directory
-*_build
+_build/
 
 # a.out
-*a.out
+a.out
 
 # configuration file
 *.vscode
diff --git a/src/Readme_for_developers.src.md b/src/Readme_for_developers.src.md
index af6df0e..838288b 100644
--- a/src/Readme_for_developers.src.md
+++ b/src/Readme_for_developers.src.md
@@ -444,7 +444,7 @@ The repository not only stores source files but also shows the whole tutorial.
 Src.md files can be translated to html files.
 You need pandoc to do this.
 Most linux distribution has pandoc package.
-Refer to your distribution document to install it.
+Refer to your distribution document to install.
 
 Type `rake html` to generate html files.
 
diff --git a/src/sec1.src.md b/src/sec1.src.md
index 224c9fb..3cdd3b4 100644
--- a/src/sec1.src.md
+++ b/src/sec1.src.md
@@ -27,7 +27,7 @@ You need:
 
 - Linux.
 - Ruby programming language.
-There are two ways to install it.
+There are two ways to install.
 One is installing the distribution's package.
 The other is using rbenv and ruby-build.
 If you want to use the latest version of ruby, use rbenv.
@@ -41,7 +41,7 @@ GTK4-tutorial repository contains tutorial documents and programs such as conver
 All of them make up the 'GTK4-tutorial' package.
 This package is simply called 'GTK4-tutorial' in the following description.
 
-GTK4-tutorial is free; you can redistribute it and/or modify it under terms of the following licenses.
+GTK4-tutorial is free; you can redistribute it and/or modify it under the terms of the following licenses.
 
 - The license of documents in GTK4-tutorial is the GNU Free Documentation License as published by the Free Software Foundation; either version 1.3 of the License or, at your opinion, any later version.
 The documents are Markdown, HTML and image files.
diff --git a/src/sec21.src.md b/src/sec21.src.md
index a7e7d24..87bc1e4 100644
--- a/src/sec21.src.md
+++ b/src/sec21.src.md
@@ -177,7 +177,7 @@ Otherwise the unit is point.
 ## GSettings
 
 We want to maintain the font data after the application quits.
-There are some ways to implement it.
+There are some ways to implement.
 
 - Make a configuration file.
 For example, a text file "~/.config/tfe/font_desc.cfg" keeps font information.
diff --git a/src/sec32.src.md b/src/sec32.src.md
index 3f55527..670b667 100644
--- a/src/sec32.src.md
+++ b/src/sec32.src.md
@@ -130,7 +130,7 @@ The function is given the item (GFileInfo) of the GtkSortListModel as an argumen
 But you need to be careful that it can be NULL while the list item is being recycled.
 So, `G_IS_FILE_INFO (info)` is always necessary in callback functions.
 The function retrieves a filename from `info`.
-The string is owned by `info` so it is necessary to duplicate it.
+The string is owned by `info` so it is necessary to duplicate.
 And it returns the copied string.
 
 GtkNumericSorter compares numbers.