diff --git a/Concurrent Systems/notes/13 - Weak Bisimilarity.md b/Concurrent Systems/notes/13 - Weak Bisimilarity.md
index 83e71bb..9bc9f22 100644
--- a/Concurrent Systems/notes/13 - Weak Bisimilarity.md	
+++ b/Concurrent Systems/notes/13 - Weak Bisimilarity.md	
@@ -137,4 +137,5 @@ termination via action $b_i$
 
 The specification is:
 if $i \in X$ then:
-$$Si,X=a_{i}.S_{(i \space mod \spac)}$$
\ No newline at end of file
+$$S_{i,X}=\sum_{j \in X}b_{j}.S_{i,X-\{ j \}}$$
+otherwise: $$S_{i,X}=a_{i}.S_{(i \space mod \space n)+1,X\cup \{ i \}} + \sum_{j \in X}b_{j}.S_{i,X-\{ j \}}$$