diff --git a/Concurrent Systems/notes/4b -.md b/Concurrent Systems/notes/4b -.md
index 2928348..d11cef5 100644
--- a/Concurrent Systems/notes/4b -.md	
+++ b/Concurrent Systems/notes/4b -.md	
@@ -68,5 +68,24 @@ operation begin_read() :=
 	if AW != 0 then
 		CR.wait()
 		CR.signal()
+	AR++
+	WR--
+
+operation end_read() :=
+	AR--
+	if AR + WR = 0 then
+		CW.signal()
+
+operation begin_write() :=
+	if (AR+WR != 0 or AW != 0) then
+		CW.wait()
+	AW++
+
+operation end_write() :=
+	AW--
+	if WR > 0 then
+		CR.signal()
+	else
+		CW.signal()
 
 ```
\ No newline at end of file