diff --git a/School/Analyse/Periode 2/Week 1.md b/School/Analyse/Periode 2/Week 1.md
index 6155c51..7e8996d 100644
--- a/School/Analyse/Periode 2/Week 1.md	
+++ b/School/Analyse/Periode 2/Week 1.md	
@@ -111,10 +111,29 @@ These bugs are hard to detect and fix.
 # Correctness
 Sequetial programs wil always give the same result. Debugging makes sense.
 
-Concurrent programs do not behave like this. Some instances may give correct output and some not. 
-
-
-
+Concurrent programs do not behave like this. Some instances may give correct output and some not. (Without protections)
+
+This implies that we cannot debug a concurrent program in the  
+normal way, because each time we run the program, we will likely  
+have a different order of interleaving.
+
+Correctness of (non-terminating) concurrent programs is defined in  
+terms of properties of computations, rather than a functional result.
+
+Types:
+- Safety properties: the property must always be true.
+	Example: Always, mouse cursor is displayed.
+	
+- Liveness properties: The property must become true at some point.
+	Example: Click with a mouse, eventually the mouse cursor changes.
+	
+# Fairness
+Arbitrary interleaving assumes no order of speed executing statements for diffrent processes/tasks.
+- However, it does not make sense to assume that statements from any  
+specific process are never selected in the interleaving.
+
+A scenario of executing statements is (weakly) fair if a statement that  
+is continually enabled, eventually is selected to execute.