Add optimality note: exhaustive enumeration confirms magnitude 5 is minimum

README.md

@@ -83,6 +83,10 @@ NAND is permissive (7 of 8 pass). NOR is restrictive (1 of 8 passes).
 | Bias | +2 |
 | **Total** | **4 parameters** |
 
+## Optimality
+
+Exhaustive enumeration of all 681 weight configurations at magnitudes 0-5 confirms this circuit is **already at minimum magnitude (5)**. There is exactly one valid configuration at magnitude 5, and no valid configurations exist below it.
+
 ## Usage
 
 ```python