diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index 827bc21..b752c08 100644
--- a/.obsidian/workspace.json
+++ b/.obsidian/workspace.json
@@ -51,9 +51,9 @@
               "type": "pdf",
               "state": {
                 "file": "Concurrent Systems/slides/class 7.pdf",
-                "page": 9,
+                "page": 10,
                 "left": -23,
-                "top": 171,
+                "top": 175,
                 "zoom": 0.680522565320665
               },
               "icon": "lucide-file-text",
@@ -237,6 +237,7 @@
   "lastOpenFiles": [
     "Concurrent Systems/slides/class 7.pdf",
     "Concurrent Systems/notes/7- MUTEX-free concurrency.md",
+    "Pasted image 20250324100652.png",
     "Pasted image 20250324092633.png",
     "Pasted image 20250324091452.png",
     "Concurrent Systems/notes/Pasted image 20250324082534.png",
@@ -265,7 +266,6 @@
     "Pasted image 20250318090733.png",
     "Concurrent Systems/slides/class 5.pdf",
     "Concurrent Systems/notes/images/Pasted image 20250317105355.png",
-    "Concurrent Systems/notes/images/Pasted image 20250317100456.png",
     "HCIW/slides/4 HUI2016-6-forcefeedback.pdf",
     "HCIW/slides/3b Haptic slides.pdf",
     "HCIW/slides/3Haptic interaction.pdf",
diff --git a/Concurrent Systems/notes/7- MUTEX-free concurrency.md b/Concurrent Systems/notes/7- MUTEX-free concurrency.md
index 07f7a62..ec8fe73 100644
--- a/Concurrent Systems/notes/7- MUTEX-free concurrency.md	
+++ b/Concurrent Systems/notes/7- MUTEX-free concurrency.md	
@@ -144,7 +144,15 @@ This is needed for the so called ABA problem with compare&set:
 	if X.compare&set(tmp, v) then ...
 ```
 - this is to ensure that the value of X has not changed in the computation
-- the problem is that X can be changed twice before compare&set
+- the problem is that X can be changed twice before compare&set (e.g. it was A, it became B and than came back to A)
 - solution: X is a pair ⟨val , seq_numb⟩, with the constraint that each modification of X increases its sequence_number
 	- with the compare&set you mainly test that the sequence_number has not changed
 
+TOP : a register that can be read or compare&setted
+	![[Pasted image 20250324100652.png]]
+
+```
+push(w) :=
+	while true do ⟨i,v,s⟩ <- TOP
+	conclude(i,v,s) if i=k then return FULL newtop ß ⟨i+1,w,STACK[i+1].seq_num+1⟩ if TOP.compare&set(⟨i,v,s⟩,newtop) then return OK
+```
\ No newline at end of file
diff --git a/Pasted image 20250324100652.png b/Pasted image 20250324100652.png
new file mode 100644
index 0000000..ff95fe8
Binary files /dev/null and b/Pasted image 20250324100652.png differ