diff -rN -u old-darcs-book/en/04-happy-little-accidents.md new-darcs-book/en/04-happy-little-accidents.md
--- old-darcs-book/en/04-happy-little-accidents.md	2024-11-24 04:48:48.828030338 +0000
+++ new-darcs-book/en/04-happy-little-accidents.md	2024-11-24 04:48:48.828030338 +0000
@@ -118,3 +118,56 @@
 
 And just like that, we have undone our `revert`. Isn't it nice to have an extra
 safe guard just in case something goes wrong?
+
+Roll-over! Roll-over! Roll-back! `rollback`!
+--------------------------------------------
+
+Another nice property of `darcs` is that every change has an inverse. Oh boy,
+math jargon again. Let me explain. A change describes something we have… well
+changed *duh*. Let's say we have added a line "happy happy joy joy" to a file.
+The inverse of that change  would be removing that line. So when you apply the
+inverse of a change, it takes back all the modifications of that that change.
+You can once again think of it in terms of numbers. When you have `x + 3` you
+are adding `3` to some number `x`. You can get back to `x` by applying the
+inverse of `3` which is `-3`. It's the same idea, just with changes.
+
+```
+$ echo "happy happy joy joy" >> story.txt
+$ darcs record -m 'add some joy'
+$ darcs log -v -p joy
+patch 5ac28c7924511e5fffaf1f028b89158c429938a8
+Author: raichoo@example.com
+Date:   Wed Jun 27 16:31:28 CEST 2018
+  * add some joy
+    hunk ./story.txt 2
+    +happy happy joy joy
+```
+
+So, a couple of weeks later we figure that maybe this is just way too much joy
+and we decide to roll back the change. We do that by using `darcs rollback`
+which takes some changes and applies their inverse to the working tree. Just
+like `log` `rollback` can take a `-p` flag to specify a pattern for selecting
+matching patches. I know that the package name contains the word "joy" so I'm
+using that.
+
+```
+$ darcs rollback -p joy
+patch 5ac28c7924511e5fffaf1f028b89158c429938a8
+Author: raichoo@example.com
+Date:   Wed Jun 27 16:31:28 CEST 2018
+  * add some joy
+Shall I rollback this patch? (1/1)  [ynW...], or ? for more options: y
+Do you want to Rollback these patches? [Yglqk...], or ? for more options: y
+hunk ./story.txt 2
++happy happy joy joy
+Shall I rollback this change? (1/1)  [ynW...], or ? for more options: y
+Do you want to Rollback these changes? [Yglqk...], or ? for more options: y
+Changes rolled back in working directory
+$ darcs whatsnew
+hunk ./story.txt 2
+-happy happy joy joy
+```
+
+`rollback` does not create any new patches, it just applies the inverses of the
+changes you have selected to your working tree, it's up to you to record a new
+patch from them.