diff --git a/literature/2021-04-04-11-24-56.org b/literature/2021-04-04-11-24-56.org
index 821c96b..6ca946a 100644
--- a/literature/2021-04-04-11-24-56.org
+++ b/literature/2021-04-04-11-24-56.org
@@ -3,7 +3,7 @@
 :END:
 #+title: Learning how to learn
 #+date: "2021-04-04 11:24:56 +08:00"
-#+date_modified: "2021-05-08 19:05:06 +08:00"
+#+date_modified: "2021-05-12 14:10:04 +08:00"
 #+language: en
 #+source: https://www.coursera.org/learn/learning-how-to-learn
 #+tags: courses personal-info-management
@@ -264,6 +264,12 @@ Your brain is composed of neuromodulators and chemicals that affects your learni
 Emotions and cognition are related to one another and no less important to learning.
 If you want to be an effective learner, you have to be happy or in the mood.
 
+Some tips for a happier brain:
+
+- Exercise.
+  Interestingly, while new neurons does appear in our, it can disappear once it is not used.
+  It can survive by remembering and creating new experiences but exercise can help in surviving newer neurons.
+
 
 
 
@@ -323,6 +329,21 @@ Nonetheless, there are ways how to start and override your habits.
 
 
 
+* Week 4
+
+- imposter syndrome, the feeling of incompetence
+- analogies and models, while not perfect, is a great way of making sure you understand and put it in your memory for a longer time
+  + science is, after all, mostly made up of models that eventually break down
+- having a whiff of ADHD-like behavior of shifting attention even if you don't want to can help in making new connections
+- people learn by trying to make sense of information rather than someone telling them
+- changing underlying thoughts can make for a better learning
+  + while empathy is beneficial, it is great to practice into filtering other people who are malicious or criticizing for the sake of undercutting
+  + or you can turn it around and make it as your motivation
+- study groups are also great but don't turn it into a socializing session
+
+
+
+
 * Takeaways from "Interview with Dr. Terrence Sejnowski"
 
 - Learn headfirst in a new topic by getting involved with peers and experts who are already invested in similar topics.
@@ -349,7 +370,6 @@ Nonetheless, there are ways how to start and override your habits.
 
 
 * Takeaways from "Interview with Dr. Robert Bilder on creativity and problem solving"
-
 - The criteria of creativity mostly applies to what is unique to you.
   It doesn't mean that others solve it that you're not creative as long as you've solved it yourself.
 
diff --git a/literature/2021-04-29-18-27-29.org b/literature/2021-04-29-18-27-29.org
index da9d0e4..544470d 100644
--- a/literature/2021-04-29-18-27-29.org
+++ b/literature/2021-04-29-18-27-29.org
@@ -3,13 +3,21 @@
 :END:
 #+title: Fundamentals of music theory
 #+date: "2021-04-29 18:27:29 +08:00"
-#+date_modified: "2021-05-09 22:02:51 +08:00"
+#+date_modified: "2021-05-10 19:15:02 +08:00"
 #+language: en
 #+source: https://www.coursera.org/learn/edinburgh-music-theory/
 
+#+name: lilypond-paper-config
+#+begin_src lilypond
+\paper {
+  indent=10\mm
+  oddFooterMarkup=##f
+}
+#+end_src
+
 
 The course took notes from the Edinburgh's course for musical theory.
-Keep in mind this course mainly deals with western musical concepts and notations.
+Keep in mind this course mainly deals with western musical concepts and notations called Common Practice.
 
 
 
@@ -38,8 +46,53 @@ Keep in mind this course mainly deals with western musical concepts and notation
   When the distance of each note is 2 semitone, it is considered as a tone.
 
 #+ATTR_ORG: :width 550
-[[file:assets/2021-04-29-18-27-29/fds-visual-octaves-and-tones.webp]]
+[[file:assets/2021-04-29-18-27-29/fds-visual-octaves-and-tones.png]]
 
 - an interval is two pitches with a certain distance
   + starting from a note, the number of tones distanced between them is the name of an interval
   + e.g., C and D is a second, C to E is a third, D to G is a fourth, F to C is a fifth
+
+- scales is a group of notes that give the flavor of the music (e.g., melancholic, gleeful)
+  + also describes the relationship of each note
+  + each scale has a tonic which usually named after the first note
+  + the common type of scales introduced are the diatonic scales, made up of seven notes with two semitones and five tones in it
+  + e.g., the C scale is made up of the notes C, D, E, F, G, A, B, C has a pattern of TTSTTTS (tone = T, semitone = S)
+  + a major scale has a pattern of TTSTTTS, a minor scale has a pattern of TSTTSTT
+  + different tonics = different pattern of semitones and tones = different quality and flavor = different melodies
+  + each of tonics in diatonic scale is called a mode (e.g., A is called Aeolian mode, E is Phrygian)
+  + Aeolian mode is a natural minor mode (has a pattern of TSTTSTT)
+
+#+begin_src lilypond  :file modes.png
+<<lilypond-paper-config>>
+{
+  \set Staff.instrumentName = #"Aeolian"
+  \relative a' { a b c d e f g a }
+  \addlyrics { A B C D E F G A }
+}
+
+{
+  \set Staff.instrumentName = #"Ionian"
+  \relative c' { c d e f g a b c }
+  \addlyrics { C D E F G A B C }
+}
+#+end_src
+
+#+results:
+[[file:assets/2021-04-29-18-27-29/modes.png]]
+
+- chords are three or more notes played together
+  + when played with three, it is considered a triad
+  + perfect fifth + major third = major triad (Cmaj)
+  + perfect fifth + minor third = minor triad (Cmin)
+  + perfect fifth + diminished third = diminished triad (Cdim)
+  + triads are also named with the lowest notes so a triad of C, E, and G is a C triad
+  + but it is a C major triad (written as Cmaj) since C and E is a major third and C, E, and G is a perfect fifth
+  + primary major chords: tonic, dominant, subdominant
+
+#+begin_src lilypond  :file chords.png
+<<lilypond-paper-config>>
+\chordmode { c1 d e f g a b }
+#+end_src
+
+#+results:
+[[file:assets/2021-04-29-18-27-29/chords.png]]
diff --git a/literature/assets/2021-04-29-18-27-29/chords-1.eps b/literature/assets/2021-04-29-18-27-29/chords-1.eps
new file mode 100644
index 0000000..40a8c34
Binary files /dev/null and b/literature/assets/2021-04-29-18-27-29/chords-1.eps differ
diff --git a/literature/assets/2021-04-29-18-27-29/chords-systems.count b/literature/assets/2021-04-29-18-27-29/chords-systems.count
new file mode 100644
index 0000000..56a6051
--- /dev/null
+++ b/literature/assets/2021-04-29-18-27-29/chords-systems.count
@@ -0,0 +1 @@
+1
\ No newline at end of file
diff --git a/literature/assets/2021-04-29-18-27-29/chords-systems.texi b/literature/assets/2021-04-29-18-27-29/chords-systems.texi
new file mode 100644
index 0000000..cbe3587
--- /dev/null
+++ b/literature/assets/2021-04-29-18-27-29/chords-systems.texi
@@ -0,0 +1,2 @@
+@image{chords-1}
+@c eof
diff --git a/literature/assets/2021-04-29-18-27-29/chords.png b/literature/assets/2021-04-29-18-27-29/chords.png
new file mode 100644
index 0000000..c56925e
Binary files /dev/null and b/literature/assets/2021-04-29-18-27-29/chords.png differ
diff --git a/literature/assets/2021-04-29-18-27-29/modes-1.eps b/literature/assets/2021-04-29-18-27-29/modes-1.eps
new file mode 100644
index 0000000..f4f8fc7
Binary files /dev/null and b/literature/assets/2021-04-29-18-27-29/modes-1.eps differ
diff --git a/literature/assets/2021-04-29-18-27-29/modes-systems.count b/literature/assets/2021-04-29-18-27-29/modes-systems.count
new file mode 100644
index 0000000..56a6051
--- /dev/null
+++ b/literature/assets/2021-04-29-18-27-29/modes-systems.count
@@ -0,0 +1 @@
+1
\ No newline at end of file
diff --git a/literature/assets/2021-04-29-18-27-29/modes-systems.texi b/literature/assets/2021-04-29-18-27-29/modes-systems.texi
new file mode 100644
index 0000000..b8a2ea1
--- /dev/null
+++ b/literature/assets/2021-04-29-18-27-29/modes-systems.texi
@@ -0,0 +1,2 @@
+@image{modes-1}
+@c eof
diff --git a/literature/assets/2021-04-29-18-27-29/modes.png b/literature/assets/2021-04-29-18-27-29/modes.png
new file mode 100644
index 0000000..3e769ad
Binary files /dev/null and b/literature/assets/2021-04-29-18-27-29/modes.png differ
diff --git a/structured/assets/lang.lilypond/chords-1.eps b/structured/assets/lang.lilypond/chords-1.eps
new file mode 100644
index 0000000..0edc7a6
Binary files /dev/null and b/structured/assets/lang.lilypond/chords-1.eps differ
diff --git a/structured/assets/lang.lilypond/chords-systems.count b/structured/assets/lang.lilypond/chords-systems.count
new file mode 100644
index 0000000..56a6051
--- /dev/null
+++ b/structured/assets/lang.lilypond/chords-systems.count
@@ -0,0 +1 @@
+1
\ No newline at end of file
diff --git a/structured/assets/lang.lilypond/chords-systems.texi b/structured/assets/lang.lilypond/chords-systems.texi
new file mode 100644
index 0000000..cbe3587
--- /dev/null
+++ b/structured/assets/lang.lilypond/chords-systems.texi
@@ -0,0 +1,2 @@
+@image{chords-1}
+@c eof
diff --git a/structured/assets/lang.lilypond/chords.png b/structured/assets/lang.lilypond/chords.png
new file mode 100644
index 0000000..d35fbf7
Binary files /dev/null and b/structured/assets/lang.lilypond/chords.png differ
diff --git a/structured/assets/lang.lilypond/notes-1.eps b/structured/assets/lang.lilypond/notes-1.eps
new file mode 100644
index 0000000..3ac8626
Binary files /dev/null and b/structured/assets/lang.lilypond/notes-1.eps differ
diff --git a/structured/assets/lang.lilypond/notes-systems.count b/structured/assets/lang.lilypond/notes-systems.count
new file mode 100644
index 0000000..56a6051
--- /dev/null
+++ b/structured/assets/lang.lilypond/notes-systems.count
@@ -0,0 +1 @@
+1
\ No newline at end of file
diff --git a/structured/assets/lang.lilypond/notes-systems.texi b/structured/assets/lang.lilypond/notes-systems.texi
new file mode 100644
index 0000000..4e26702
--- /dev/null
+++ b/structured/assets/lang.lilypond/notes-systems.texi
@@ -0,0 +1,2 @@
+@image{notes-1}
+@c eof
diff --git a/structured/assets/lang.lilypond/notes.png b/structured/assets/lang.lilypond/notes.png
new file mode 100644
index 0000000..cab4a3b
Binary files /dev/null and b/structured/assets/lang.lilypond/notes.png differ
diff --git a/structured/lang.lilypond.org b/structured/lang.lilypond.org
new file mode 100644
index 0000000..d5b74aa
--- /dev/null
+++ b/structured/lang.lilypond.org
@@ -0,0 +1,44 @@
+#+title: Lilypond
+#+date: "2021-05-10 19:36:43 +08:00"
+#+date_modified: "2021-05-10 20:25:17 +08:00"
+#+language: en
+#+property: header-args:lilypond  :exports both
+
+
+The LaTeX of music notation.
+It is a formatting language for music notation that has to be compiled into various output formats.
+The input file is a plain-text file making it very good with version control systems.
+
+
+
+
+* Notes, chords, and scales
+
+#+begin_src lilypond  :file notes.png
+<<lilypond-paper>>
+{ c d e f g a b c' }
+\relative d' { c d e f g a b c' }
+#+end_src
+
+#+results:
+[[file:assets/lang.lilypond/notes.png]]
+
+#+begin_src lilypond  :file chords.png
+<<lilypond-paper>>
+\chordmode { c1 d e f g a b c' }
+#+end_src
+
+#+results:
+[[file:assets/lang.lilypond/chords.png]]
+
+
+
+* Paper configuration
+
+#+name: lilypond-paper
+#+begin_src lilypond  :exports none
+\paper {
+  indent=10\mm
+  oddFooterMarkup=##f
+}
+#+end_src
diff --git a/structured/lang.oil.org b/structured/lang.oil.org
new file mode 100644
index 0000000..51f2cab
--- /dev/null
+++ b/structured/lang.oil.org
@@ -0,0 +1,55 @@
+#+title: Oil shell
+#+date: "2021-05-09 16:40:50 +08:00"
+#+date_modified: "2021-05-10 11:25:10 +08:00"
+#+language: en
+
+
+For future references, this note mainly notes Oil v0.8.7 and later versions.
+
+
+
+
+* What is Oil shell?
+
+A modern shell attempting the replace Bash slowly.
+The project has an ambitious goal with a wide scope.
+It is known for its shell-oriented blog and the developer is very responsive and active with shell-related posts.
+
+While there are multiple components in this project, we're focusing on two: *OSH and Oil shell*.
+
+- *OSH is the bridge between Bash and Oil.*
+  It aims to be the most Bash-compatible shell that you can run most Bash scripts just fine.
+  The point of this component is improving what's under the hood, imposing sensible defaults on them, and getting a wide reach since Bash is the most popular shell.
+  While it may not run every Bash script in existence, the other point is to require minimal rewrites to run it with OSH.
+
+- *Oil shell is the modern replacement of Bash* from its syntax and behavior.
+  It aims to be the shell for people familiar to Python, Ruby, JavaScript, and the like.
+  This is the other side of the bridge that OSH aims to reach.
+
+
+
+
+
+* Tips and tricks
+
+- You can make an array so far with ~var x = %()~.
+
+- To push for an array, use ~push :ARRAY_VAR $ITEMS...~.
+
+- Oil has two main syntactic modes: command and expression mode.
+  Command mode is more like Bash while expression mode is more like Python.
+  This is how Oil can make a rich and expressive scripting that is closer to the shell.
+
+- Oil will go into expression mode in few places:
+  + In RHS of an assignment expression.
+  + In ~if~ statements (e.g., ~if ($EXPR) { echo "WHOA" }~).
+  + Interpolated Oil expressions with ~$[]~ (e.g., ~$[true]~, ~$[len(ARGV)~).
+
+- Oil can parse different modes, making it possible to create DSLs and to deal with the complex syntax of the shell.
+
+- You can also create an array with ~[]~.
+  The ~%()~ is more like for an array of objects.
+
+- You can enter into expression mode with ~_~.
+  Although, this simply ignores the expression and will not be printed.
+  Still pretty useful.
diff --git a/structured/shell.oil.org b/structured/shell.oil.org
deleted file mode 100644
index 27e7df1..0000000
--- a/structured/shell.oil.org
+++ /dev/null
@@ -1,46 +0,0 @@
-#+title: Oil shell
-#+date: "2021-05-09 16:40:50 +08:00"
-#+date_modified: "2021-05-09 17:15:03 +08:00"
-#+language: en
-
-
-For future references:
-
-#+begin_src sh  :results output
-oil --version
-#+end_src
-
-#+RESULTS:
-: Oil version 0.8.7
-: Release Date: 2021-01-23 07:35:11+00:00
-: Arch: x86_64
-: OS: Linux
-: Platform: #13~1617215757~20.10~97a8d1a-Ubuntu SMP Thu Apr 1 21:09:17 UTC 2
-: Compiler: GCC 10.2.0
-: Interpreter: OVM
-: Interpreter version: 2.7.13
-: Bytecode: bytecode-opy.zip
-
-This version contains incomplete implementation and documentation which is why I'm noting it here.
-
-- You can make an array so far with ~var x = %()~.
-
-- To push for an array, use ~push :ARRAY_VAR $ITEMS...~.
-
-- Oil has two main syntactic modes: command and expression mode.
-  Command mode is more like Bash while expression mode is more like Python.
-  This is how Oil can make a rich and expressive scripting that is closer to the shell.
-
-- Oil will go into expression mode in few places:
-  + In RHS of an assignment expression.
-  + In ~if~ statements (e.g., ~if ($EXPR) { echo "WHOA" }~).
-  + Interpolated Oil expressions with ~$[]~ (e.g., ~$[true]~, ~$[len(ARGV)~).
-
-- Oil can parse different modes, making it possible to create DSLs and to deal with the complex syntax of the shell.
-
-- You can also create an array with ~[]~.
-  The ~%()~ is more like for an array of objects.
-
-- You can enter into expression mode with ~_~.
-  Although, this simply ignores the expression and will not be printed.
-  Still pretty useful.