diff --git a/_subsections/lesson-03.org b/_subsections/lesson-03.org
index 0bbc9de..c0fd1dd 100644
--- a/_subsections/lesson-03.org
+++ b/_subsections/lesson-03.org
@@ -26,7 +26,7 @@
 + [[https://youtu.be/a6Q8Na575qc?si=gyYNZk4_XiXVk_4a&t=1217][20:17 - movement keys]]
 + [[https://youtu.be/a6Q8Na575qc?si=QysgH5bMEG0bigKq&t=1530][25:30 - editing commands]]
 + [[https://youtu.be/a6Q8Na575qc?si=_gbAQlOZ_irCdHt6&t=1797][29:54 - questions]]
-+ [[https://youtu.be/a6Q8Na575qc?si=4VwNEC040Jna5znz&t=2254][37:33 - demo]] *current*
++ [[https://youtu.be/a6Q8Na575qc?si=4VwNEC040Jna5znz&t=2254][37:33 - demo]]
 + [[https://youtu.be/a6Q8Na575qc?si=0qDOcyT0WX1U4RXB&t=2682][44:42 - vim configuration]]
 
 * notes
diff --git a/_subsections/lesson-04.org b/_subsections/lesson-04.org
new file mode 100644
index 0000000..218ede6
--- /dev/null
+++ b/_subsections/lesson-04.org
@@ -0,0 +1,48 @@
+#+title: Lesson 04 | Data Wrangling
+#+HTML_HEAD: <link rel="stylesheet" type="text/css" href="../_share/media/css/missing-semester.css" />
+#+HTML_HEAD: <link rel="stylesheet" type="text/css" href="../_share/media/css/org-media-sass/collapsible.css" />
+#+HTML_HEAD: <script src="../_share/media/js/collapsible.js"></script>
+#+OPTIONS: H:6
+
+* Links
+#+attr_html: :class links
+- [[../toc.org][TOC | Missing Semester]]
+- [[https://www.youtube.com/playlist?list=PLyzOVJj3bHQuloKGG59rS43e29ro7I57J][Playlist: Missing Semester]]
+- [[https://missing.csail.mit.edu/2020/data-wrangling/][class notes]]
+
+- Curr: https://youtu.be/sz_dsktIjt4?si=BekzMmns2yPtCWOz
+
+
+*** timestamps
+:PROPERTIES:
+:CUSTOM_ID: timestamp
+:END:
+
+#+attr_html: :class playlist
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=4s][00:00 - introduction]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=415s][06:55 - Stream Editor]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=456s][07:36 - Replacement Expressions]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=538s][08:58 - Regular Expression]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=560s][09:20 - Regular Expressions]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=620s][10:20 - Square Brackets]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=693s][11:33 - Add Modifiers]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=776s][12:56 - Alternations]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=1029s][17:09 - Anchoring the Regular Expression]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=1138s][18:58 - Capture Groups]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=1215s][20:15 - Regular Expression Debugger]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=1450s][24:10 - Regular Sessions]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=1561s][26:01 - Match and Email Address ]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=1743s][29:03 - Sort]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2040s][34:00 - Awk]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2324s][38:44 - Berkeley Calculator]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2437s][40:37 - Computer Statistics over Inputs]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2482s][41:22 - Summary Statistics]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2513s][41:53 - Plotting]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2570s][42:50 - Two sort of special types]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2754s][45:54 - example where data wrangling is useful]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2805s][46:45 - image captures to standard output]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2846s][47:26 - operate on standard input]]
++ [[https://www.youtube.com/watch?v=sz_dsktIjt4&t=2880s][48:00 - display in an image display]]
+
+* notes
+