diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index 2827bcd..827bc21 100644
--- a/.obsidian/workspace.json
+++ b/.obsidian/workspace.json
@@ -51,9 +51,9 @@
               "type": "pdf",
               "state": {
                 "file": "Concurrent Systems/slides/class 7.pdf",
-                "page": 8,
+                "page": 9,
                 "left": -23,
-                "top": 103,
+                "top": 171,
                 "zoom": 0.680522565320665
               },
               "icon": "lucide-file-text",
diff --git a/Concurrent Systems/notes/7- MUTEX-free concurrency.md b/Concurrent Systems/notes/7- MUTEX-free concurrency.md
index 43d41d7..6ec93e1 100644
--- a/Concurrent Systems/notes/7- MUTEX-free concurrency.md	
+++ b/Concurrent Systems/notes/7- MUTEX-free concurrency.md	
@@ -128,4 +128,14 @@ pop() :=
 ```
 
 REMARK: crashes do not compromise progress!
-PROBLEM: unboundedness of REG is not realistic
\ No newline at end of file
+PROBLEM: unboundedness of REG is not realistic
+
+### A Non-blocking Bounded Stack
+Idea: every operation is started by the invoking process and finalized by the next process
+
+`STACK[0...k]` : an array of registers that can be read or compare&setted
+	`STACK[i]` is actually a pair ⟨val , seq_numb⟩ initialized at ⟨⊥,0⟩
+
+This is needed for the so called ABA problem with compare&set:
+- A typical use of compare&set is
+  ```stm```
\ No newline at end of file