diff --git a/Concurrent Systems/notes/14 Checking bisimilarity, an inference system.md b/Concurrent Systems/notes/14 Checking bisimilarity, an inference system.md
index 1e8cd1d..730bbcb 100644
--- a/Concurrent Systems/notes/14 Checking bisimilarity, an inference system.md	
+++ b/Concurrent Systems/notes/14 Checking bisimilarity, an inference system.md	
@@ -74,7 +74,7 @@ The behavior of such a server can be implemented by three processes in parallel:
 
 $$S \triangleq send.\overline{put} \quad M \triangleq put.\overline{go} \quad R \triangleq go.\overline{rcv}$$
 $$Impl \triangleq (S|M|R)\setminus\{put, go\}$$
-exercise: prove the weak bisimilarity
+exercise: prove the weak bisimilarity between the spec and the implementation.
 
 Let us consider the parallel of processes M and R, by using the axiom for parallel, we have $$\vdash M|R=put.(\overline{go}|R)+go.(M|\overline{rcv})$$
 By using the same axiom to the parallel of the three processes, we obtain