diff --git a/Concurrent Systems/notes/13 - CCS cose varie.md b/Concurrent Systems/notes/13 - CCS cose varie.md
index d7fd612..cbce05c 100644
--- a/Concurrent Systems/notes/13 - CCS cose varie.md	
+++ b/Concurrent Systems/notes/13 - CCS cose varie.md	
@@ -61,4 +61,7 @@ where M denotes a sum.
 An equivalence relation $R$ is a congruence if and only if
 $$\forall (P, Q) \in R, \forall C.(C[P], C[Q]) \in R$$
 Is bisimilarity a congruence? Yes.
-$$$$
\ No newline at end of file
+**Theorem:**
+$$if \space P ∼ Q \space then \space \forall C.C[P] ∼ C[Q]$$
+
+Proof on the slides.
\ No newline at end of file