diff --git a/Concurrent Systems/notes/3.md b/Concurrent Systems/notes/3.md
index 70ae8d5..50990ad 100644
--- a/Concurrent Systems/notes/3.md	
+++ b/Concurrent Systems/notes/3.md	
@@ -110,4 +110,10 @@ unlock() :=
 ### Safe registers
 Atomic R/W and specialized HW primitives provide some form of atomicity. But is it possible to enforce MUTEX without atomicity?
 
-A **MRMW Safe register** is a register that provides READ and
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+A **MRSW Safe register** is a register that provides READ and WRITE such that:
+1. every READ that does not overlap with a WRITE returns the value stored in the register
+2. a READ that overlaps with a WRITE can return **any possible value** (of the register domain).
+
+A **MRMW Safe register** behaves like a MRSW safe register, when WRITE operations do not overlap. Otherwise, in case of overlapping WRITEs, the register can contain any value (of the register domain).
+
+This is the weakest type of register that is useful in concurrency.
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