diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index a569f6b..3dbd8f9 100644
--- a/.obsidian/workspace.json
+++ b/.obsidian/workspace.json
@@ -230,6 +230,7 @@
   "lastOpenFiles": [
     "Concurrent Systems/slides/class 12.pdf",
     "Concurrent Systems/notes/13 - CCS cose varie.md",
+    "Pasted image 20250415090109.png",
     "Concurrent Systems/notes/12 - Calculus of communicating system.md",
     "Pasted image 20250415082906.png",
     "Concurrent Systems/notes/11 - LTSs and Bisimulation.md",
@@ -242,7 +243,6 @@
     "Concurrent Systems/notes/images/Pasted image 20250414152247.png",
     "Concurrent Systems/notes/images/Pasted image 20250414152234.png",
     "Concurrent Systems/notes/images/Pasted image 20250414152221.png",
-    "Concurrent Systems/notes/images/Pasted image 20250414104010.png",
     "HCIW/notes/3 - Beacons.md",
     "HCIW/slides/Zooming interfaces.pdf",
     "HCIW/slides/Gestural interaction.pdf",
diff --git a/Concurrent Systems/notes/13 - CCS cose varie.md b/Concurrent Systems/notes/13 - CCS cose varie.md
index 8ba455a..7d7e55c 100644
--- a/Concurrent Systems/notes/13 - CCS cose varie.md	
+++ b/Concurrent Systems/notes/13 - CCS cose varie.md	
@@ -47,5 +47,12 @@ Let's go!
 One of the main aims of an equivalence notion between processes is to make equational reasonings of the kind: “if P and Q are equivalent, then they can be interchangeably used in any execution context”.
 
 This feature on an equivalence makes it a *congruence*
-Not all equivalences are necessarily congruences (even though most of them are
-To properly define a congruence, we first need to define an execution context, and then what it means to run a process in a context. Intuitively:
\ No newline at end of file
+Not all equivalences are necessarily congruences (even though most of them are).
+To properly define a congruence, we first need to define an execution context, and then what it means to run a process in a context. Intuitively:
+![200](../../Pasted%20image%2020250415090109.png)
+
+where C is a context (i.e., a process with a hole ☐), P is a process, and $C[P]$ denotes filling the hole with P
+
+Example: $$if \space C = (☐ | Q) \textbackslash a, \space then \space C[P] = (P | Q) \textbackslash a$$
+The set C of CCS contexts is given by the following grammar:
+$$C ::= ☐ \space | \space C|P \space | $$
\ No newline at end of file
diff --git a/Pasted image 20250415090109.png b/Pasted image 20250415090109.png
new file mode 100644
index 0000000..805800e
Binary files /dev/null and b/Pasted image 20250415090109.png differ