diff --git a/csp/sync.csp b/csp/sync.csp
index 855cadf..b12d529 100644
--- a/csp/sync.csp
+++ b/csp/sync.csp
@@ -1,7 +1,12 @@
-channel input:{0,1,2}
+N = 3
+channel input, up, save:{0..N-1}
 
-USER(i) = input!i -> USER((i+1)%3)
-CLIENT(i) = input?j -> CLIENT(j)
-SYSTEM = USER(0) ||| CLIENT(0)
+apply(state, patch) = (state + patch) % N
+diff(state1, state2) = (state2 - state1) % N
+
+CLIENT(state, shadow) = input?new_state -> up!diff(shadow, new_state) -> CLIENT(new_state, shadow)
+SERVER(state, shadow) = 
+  up?patch -> save!apply(state, patch) -> SERVER(apply(state, patch), apply(shadow, patch))
+SYSTEM = CLIENT(0, 0) ||| SERVER(0, 0)
 
 assert SYSTEM :[deadlock free [F]]
\ No newline at end of file