# Moved to Octopress 3

## In short

Link for my new blog: https://git.io/vo3

## Motivation for giving up a large blog

As this blog grows, things have become increasingly harder to manage. The customizations, scripts and stylesheets are everywhere, within and outside the source folder. The CSS stylesheets for codeblocks and a Solarized theme were written or installed years ago. The Gist tag in Octopress doesn’t work as well as expected. It’s hard to see the highlighted area. Moreover, the range and mark in Octopress 2’s codeblock tag never works. As the purpose of this blog is to remind myself about the technical details of the code, the lack of such functionalities caused me a lot of inconveniences: while writing, after attaching the whole chuck of code, I need to specify the line number; while reading, after viewing the line number, I have to locate it in lines of code. In order to highlight part of the code, I’ve created some CSS classes (e.g. UBCli) and put it somewhere inside sass folder, I spent hours for test the rules and identified the important ! ones. This custom CSS class is fine in normal text, but it breaks in list items <li></li>. It’s time switch to Jekyll plugins written by full-time developers, such as jekyll-terminal. But then I need to install a plugin. Will it be compatible with the existing plugins/*.rb? Instead of spending even much more time on code written in a language that I don’t even understand, as a non-developer and a math student, I can choose another popular technology which is well-developped for posting math and program code.

The structure of an Octopress 3 blog repository is cleaner than that of Octopress 2 because Octopress 3 is a Ruby gem, which can be managed by bundle. This tool and Git work together to bring about an easier new feature test on the local repository for my blog.

What’s worse: due to the change of timezone last year, Google Webmasters has found over 70 crawl errors in this blog. Despite the Jekyll update to version 3, I couldn’t resolve this issue. I’ll manually fix each erroneous link later if I’ve time.

I tried hard migrating over 350 existing post in this blog to Octopress 3, but it’s too hard. First, jekyll build returned a plethora of syntax errors caused by the change in default markdown parser (from rdiscound to kramdown with GFM enabled). Second, some of the posts are about technologies that I’m no longer using now, so they aren’t worth the effort. Third, I found it extremely hard to set up the stylesheets and the Liquid templates dispersed in several separate folders (namely, sass/, _includes/, _templates/, _layouts stylesheets, javascripts), so that I can have the category list and RSS back. The sources for examples and documentations for Jekyll Liquid tags are few. I can’t even find a way to verify the example of the include tag on Shopify Liquid’s documentation. The result depends on so many factors, notably the installed version of Ruby (runtime environment and gems) and the machine’s operating system (for Windows, the wdm gem is needed). The whole process requires many commands and is certainly prone to human errors. After one week’s fruitless attempt. Being exhausted, I realised that I need to give up some nice features in the original blog, and move to the new one for a more manageable framework in order to save time.

# Ubuntu on Windows 10 Custom Display

## Background

Same as some of my recent posts: get jekyll serve working to watch for changes during a preview of my Jekyll-bootstrap blog.

Since I found the Ruby gems setup too difficult, I switched to Ubuntu on Windows 10 after reading a Ruby setup guide.

## Problem

The default display settings didn’t look great, so I installed Ubuntu Mono font. Unluckily, one can’t type Chinese characters, and the bottom line of tmux keeps jumping up from time to time. Most importantly, the copy and paste function isn’t convenient to use: every time I need to paste something, I have to move the mouse to the top of the window, then right click and select “Modify” → “Paste”. That’s too slow when compared to <S-Ins> in mintty which is shipped with Git for Windows.

However, on WLS, aptitude takes good care of package dependencies. That’s much better for installing necessary stuff for blogging with frameworks like Jekyll.

How can I run WLS using a mintty shell?

# Windows 10 Time Sync Error

I’ve tried adding a custom inbound rule in my firewall so as to allow NTP access via UDP port 123 after reading a post about firewall settings for NTP, with the aid of another post about detailed steps for opening ports on Windows 10. Before that, I had already done all steps in services.msc to allow automatic startup of the Windows Time service. Finally, I manually adjusted the time.

# Shortened GitHub URLs for This Site

## Background

I want to include a link to a Gist in an Octopress codeblock.

## Problem

In the syntax for a codeblock, the link is too long. This can cause problems in a graphical frontend of Git, such as gitk.

## Solution

I found a post about GitHub URL Shortener by accident.

$curl -i https://git.io -F "url=https://github.com/vincenttam" -F "code=vtam" % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 293 100 29 100 264 40 367 --:--:-- --:--:-- --:--:-- 375HT TP/1.1 100 Continue HTTP/1.1 201 Created Server: Cowboy Connection: keep-alive Date: Tue, 10 Jan 2017 22:50:08 GMT Status: 201 Created Content-Type: text/html;charset=utf-8 Location: https://git.io/vtam Content-Length: 29 X-Xss-Protection: 1; mode=block X-Content-Type-Options: nosniff X-Frame-Options: SAMEORIGIN X-Runtime: 0.111560 X-Node: 6a832541-d7fa-4b2b-9a4b-1e3355ad0eab X-Revision: 4fdc60de6311e6a3aa31e19bc7b3aad7e85d33a6 Strict-Transport-Security: max-age=31536000; includeSubDomains Via: 1.1 vegur https://github.com/vincenttam  In fact, git.io is much simpler for users who don’t type commands. ## Summary I created three short URLs with this tool. 1. https://git.io/vtam for my GitHub account 2. https://git.io/vtblog for this blog 3. https://git.io/vb2 for Blog 2 # A Quick Markdown Syntax Error Detection for Writing MathJax Equations in Octopress Posts (5) | Comments | ## Background In the previous post in this series, I included three Vim editor commands. ## Problem As I’ve already typed hundreds of lines of source code, I feel tired and I often make mistakes while typing those commands despite these two command mode mappings in my ~/.vimrc. # Octopress Config for Ruby 2.3 on Windows 10 | Comments | ## Motivation Same as the background in my previous article. ## Background I uninstalled Ruby 2.0 in the Control Panel, and then installed version 2.3.3 from RubyInstaller for Windows ## Problem 1: RedCloth installation failure ### Error message Gem::InstallError: The 'RedCloth' native gem requires installed build tools. Please update your PATH to include build tools or download the DevKit from 'http://rubyinstaller.org/downloads' and follow the instructions at 'http://github.com/oneclick/rubyinstaller/wiki/Development-Kit' An error occurred while installing RedCloth (4.2.9), and Bundler cannot continue. Make sure that gem install RedCloth -v '4.2.9' succeeds before bundling.  The error message is similar to Joe’s gem install error. The only difference is that I was installing RedCloth 4.9. ### Solution This failure is due to the absence of a valid path to RubyInstaller Development Kit. I tried manually adding the path to the folder for binary executables (default to C:\RubyDevKit\bin) to PATH, but it’s unsuccessful. I googled “Please update your PATH to include build tools” and found his question, whose third answer explained the function of devkitvar.bat. This batch script actually prepended the path of two folders into PATH. One is stated above; one is C:\RubyDevKit\mingw\bin. Running this batch file changes PATH temporarily. A manual configuration in the Control Panel allowed the system to detect DevKit, and this problem was thus solved. #### Already installed Name Version Number rake 10.4.2 bundler 1.13.7 #### Being installed Name Version Number With native extensions? RedCloth 4.2.9 wdm 0.1.0 blankslate 2.1.2.4 chunky_png 1.3.4 coffee-script-source 1.9.1 colorator 0.1 execjs 2.4.0 fast-stemmer 1.0.2 ffi 1.9.6 hitimes 1.2.2 jekyll-gist 1.1.0 jekyll-paginate 1.1.0 jekyll-sitemap 0.8.0 kramdown 1.6.0 liquid 2.6.2 mercenary 0.3.5 multi_json 1.11.0 posix-spawn 0.3.10 rack 1.6.0 rb-fsevent 0.9.4 redcarpet 3.2.2 safe_yaml 1.0.4 sass 3.4.13 stringex 1.4.0 tilt 1.4.1 yajl-ruby 1.2.1 ## Problem 2: wdm installation failure I put the error message from wdm in a popup dialog. Owner@Owner-PC MINGW64 /c/github/vincenttam.github.io (source)$ bundle install
Using rake 10.4.2
Using RedCloth 4.2.9
Using blankslate 2.1.2.4
Installing hitimes 1.2.2 with native extensions
Using chunky_png 1.3.4
Installing fast-stemmer 1.0.2 with native extensions
Using coffee-script-source 1.9.1
Using execjs 2.4.0
Using colorator 0.1
Using multi_json 1.11.0
Using sass 3.4.13
Using rb-fsevent 0.9.4
Using ffi 1.9.6
Using tilt 1.4.1
Using jekyll-gist 1.1.0
Using jekyll-paginate 1.1.0
Using kramdown 1.6.0
Using liquid 2.6.2
Using mercenary 0.3.5
Installing posix-spawn 0.3.10 with native extensions
Installing yajl-ruby 1.2.1 with native extensions
Installing redcarpet 3.2.2 with native extensions
Using safe_yaml 1.0.4
Using jekyll-sitemap 0.8.0
Using rack 1.6.0
Using stringex 1.4.0
Installing wdm 0.1.0 with native extensions
Using bundler 1.13.7
Installing parslet 1.5.0
Installing timers 4.0.1
Installing classifier-reborn 2.0.3
Installing coffee-script 2.3.0
Installing compass-core 1.0.3
Installing compass-import-once 1.0.5
Installing jekyll-sass-converter 1.3.0
Installing sass-globbing 1.0.0
Installing rb-inotify 0.9.5
Installing haml 4.0.6
Installing pygments.rb 0.6.2
Installing rack-protection 1.5.3
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory: C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/wdm-0.1.0/ext/wdm
C:/Ruby23-x64/bin/ruby.exe -r ./siteconf20170109-8020-1n4s35m.rb extconf.rb
checking for main() in -lkernel32... yes
checking for windows.h... yes
checking for ruby.h... yes
checking for HAVE_RUBY_ENCODING_H... yes
creating Makefile

To see why this extension failed to compile, please check the mkmf.log which can
be found here:

current directory: C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/wdm-0.1.0/ext/wdm
make "DESTDIR=" clean

current directory: C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/wdm-0.1.0/ext/wdm
make "DESTDIR="
generating wdm_ext-x64-mingw32.def
compiling entry.c
In file included from entry.c:1:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdio.h:9,
from wdm.h:1,
from entry.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from entry.c:1:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from entry.c:1:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
compiling memory.c
In file included from memory.c:1:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdio.h:9,
from wdm.h:1,
from memory.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from memory.c:1:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from memory.c:1:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
compiling monitor.c
In file included from monitor.c:1:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdio.h:9,
from wdm.h:1,
from monitor.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from monitor.c:1:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from monitor.c:1:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
compiling queue.c
In file included from queue.c:3:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
from
4-mingw32/include/_mingw_stdarg.h:14,
from
4-mingw32/include/stdarg.h:140,
from
c:\rubydevkit\mingw\bin\../lib/gcc/x86_64-w64-mingw32/4.7.2/include/stdarg.h:1,
from queue.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from queue.c:3:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from queue.c:3:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
compiling rb_change.c
In file included from rb_change.c:4:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdlib.h:9,
from rb_change.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from rb_change.c:4:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from rb_change.c:4:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
compiling rb_monitor.c
In file included from rb_monitor.c:1:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdio.h:9,
from wdm.h:1,
from rb_monitor.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from rb_monitor.c:1:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from rb_monitor.c:1:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
rb_monitor.c: In function 'rb_monitor_run_bang':
rb_monitor.c:508:9: warning: implicit declaration of function
compiling utils.c
In file included from utils.c:1:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdio.h:9,
from wdm.h:1,
from utils.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from utils.c:1:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from utils.c:1:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
compiling wdm.c
In file included from wdm.c:1:0:
wdm.h:3:0: warning: "WINVER" redefined [enabled by default]
In file included from
4-mingw32/include/crtdefs.h:10:0,
from
4-mingw32/include/stdio.h:9,
from wdm.h:1,
from wdm.c:1:
4-mingw32/include/_mingw.h:248:0:
note: this is the location of the previous definition
In file included from wdm.c:1:0:
wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
In file included from c:/Ruby23-x64/include/ruby-2.3.0/ruby/win32.h:41:0,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/defines.h:168,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby/ruby.h:36,
from c:/Ruby23-x64/include/ruby-2.3.0/ruby.h:33,
from wdm.h:12,
from wdm.c:1:
4-mingw32/include/winsock2.h:15:2:
warning: #warning Please include winsock2.h before windows.h [-Wcpp]
rb_monitor.o: In function rb_monitor_run_bang':
C:\Ruby23-x64\lib\ruby\gems\2.3.0\gems\wdm-0.1.0\ext\wdm/rb_monitor.c:508:
collect2.exe: error: ld returned 1 exit status
make: *** [wdm_ext.so] Error 1

make failed, exit code 2

Gem files will remain installed in
C:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/wdm-0.1.0 for inspection.
Results logged to
.out

An error occurred while installing wdm (0.1.0), and Bundler cannot continue.
Make sure that gem install wdm -v '0.1.0' succeeds before bundling.


From the line

wdm.h:4:0: warning: "_WIN32_WINNT" redefined [enabled by default]


I found wdm issue #18, but I failed to notice that the problem had been resolved. I later knew that from Jekyll issue #3721.

After changing the version number of wdm to 0.1.1, I could proceed further. The system output was fine.

Owner@Owner-PC MINGW64 /c/github/vincenttam.github.io (source)
$gem install wdm -v '0.1.1' Building native extensions. This could take a while... Successfully installed wdm-0.1.1 Parsing documentation for wdm-0.1.1 Installing ri documentation for wdm-0.1.1 Done installing documentation for wdm after 0 seconds 1 gem installed Owner@Owner-PC MINGW64 /c/github/vincenttam.github.io (source)$ bundle install
Resolving dependencies...
Using rake 10.4.2
Using RedCloth 4.2.9
Using blankslate 2.1.2.4
Using hitimes 1.2.2
Using chunky_png 1.3.4
Using fast-stemmer 1.0.2
Using coffee-script-source 1.9.1
Using execjs 2.4.0
Using colorator 0.1
Using multi_json 1.11.0
Using sass 3.4.13
Using rb-fsevent 0.9.4
Using ffi 1.9.6
Using tilt 1.4.1
Using jekyll-gist 1.1.0
Using jekyll-paginate 1.1.0
Using kramdown 1.6.0
Using liquid 2.6.2
Using mercenary 0.3.5
Using posix-spawn 0.3.10
Using yajl-ruby 1.2.1
Using redcarpet 3.2.2
Using safe_yaml 1.0.4
Using jekyll-sitemap 0.8.0
Using rack 1.6.0
Using stringex 1.4.0
Using wdm 0.1.1 (was 0.1.0)
Using bundler 1.13.7
Using parslet 1.5.0
Using timers 4.0.1
Using classifier-reborn 2.0.3
Using coffee-script 2.3.0
Using compass-core 1.0.3
Using compass-import-once 1.0.5
Using jekyll-sass-converter 1.3.0
Using sass-globbing 1.0.0
Using rb-inotify 0.9.5
Using haml 4.0.6
Using pygments.rb 0.6.2
Using rack-protection 1.5.3
Installing toml 0.1.2
Installing celluloid 0.16.0
Installing jekyll-coffeescript 1.0.1
Installing compass 1.0.3
Installing sinatra 1.4.5
Installing listen 2.8.5
Installing jekyll-watch 1.2.1
Installing jekyll 2.5.3
Installing octopress-hooks 2.6.0
Installing octopress-date-format 2.0.2
Bundle complete! 14 Gemfile dependencies, 50 gems now installed.
Use bundle show [gemname] to see where a bundled gem is installed.
Post-install message from compass:
Compass is charityware. If you love it, please donate on our behalf at http:
//umdf.org/compass Thanks!


## Problem 3: I have a row with Justin.

When I ran rake preview, the follow line appeared.

bash: /c/Ruby23-x64/bin/rake: C:/Users/Justin/Projects/rubyinstaller/sandbox/rub
y23_mingw/bin/ruby.exe: bad interpreter: No such file or directory


I searched “rake install justin projects” on Google. You may follow griest’s advice to have this problem fixed. If this link were unluckily dead in the future, you might leave a comment below after getting rid of Justin at the first line of /c/Ruby23-x64/bin/rake.

## Result

Octopress did work on my machine. Then I re-ran bundle install under the local repository for my another blog, but the same Celluloid error re-appeared. I don’t know how to perform a celluloid downgrade to version 16.0 under that repository. The version number for Celluloid was generated by the system—I didn’t type it in Gemfile.lock. As a result, I switched to Ubuntu on Windows 10.

# Upgraded to Git for Windows 2.11

## Background

This Git for Windows upgrade from v2.8 to v2.11 is an unsuccessful attempt to fix a Jekyll preview error on my another blog triggered by the command jekyll serve for local preview.

## Problem

After the update, I can no longer input letters with accents. Since the name of some mathematical theorems have accents, like l’Hôpital’s Rule. It would be very inconvenient if the internation keyboard can’t be used in Git Bash.

# A Comment for New Users on Math.SE

## Background

Mathematics learners ask questions on Mathematics Stack Exchange to get an answer from others without geographical or time restrictions, unlike teachers in schools. Users answer questions to gain virtual points called reputation.

## Problem

Among them, many are new users who don’t use MathJax while typing their questions. As a result, the output is difficult to read. This discourages users from answering those questions, so we would have less answers to read. Since we can sometimes benefit from alternative solutions, it’s better to post a question that is clear enough to attract others to offer an answer. We can downvote those poorly rendered questions, but I think it’s a bit cruel to do so on the very first post from new users. Therefore, I choose to leave a comment which suggests them to use $\rm \LaTeX$. They often say they don’t know how to use it. To avoid responses like that, I include a link to the MathJax guide on Meta Math.SE.

Please use $\rm \LaTeX$.

However, it’s tedious to type the markdown source code every time I want to leave this comment.

## Solution

I’ll include the code below, so that it can be simply copied and pasted next time.

# Avoided a Duplicate Question

## Problem

I encountered the following math problem, so I typed in on Mathematics Stack Exchange. Then, a list of similar posts appeared.

Let $E = {1,\dots,p}$, where $p$ is a prime number. $G$ is a transitive subgroup of $S_p$, and $H$ is a nontrivial normal subgroup of $G$. Show that $H$ acts transitively on $E$.

I notice that $\lvert G \cdot x \rvert = \lvert E \rvert = p$ because $G$ acts transitively on $E$. Now, I try to show the same for $H$, but I am stuck at $\lvert H \cdot x \rvert$. May I say that for all $g \in G$, $\lvert gH \cdot x \rvert = \lvert H \cdot x \rvert$? Why can’t $H$ fix $x$?

Is it a possible duplicate of another question?

If the answer is yes, then my post is going to be quickly flagged as duplicate by experienced users on this site, especially those who are strong at abstract algebra, and I’ll lose reputation for that.

I’ve really found the same problem on Mathematics Stack Exchange by luck.

## Lessons learnt

I viewed this question four days ago. When I tried to access it again tonight from my web browsing history, I found this a bit hard. Therefore, as a post on Mathematics Meta stack Exchange suggests, Vote early, vote often.