Day 4 done

2025/README.md

@@ -15,3 +15,10 @@ This is mostly so I can keep notes on my progress, in single markdown format so
 2. Clear history so you don't accidentally cp day1 to day2 during testing. (Undo FTW)
 3. Put the central check (Serial Valid/Invalid) in a function so it's easy to add self checks in the beginning
 
+## Lessons third day
+
+1. Can't win em all
+
+## Lessons fourth day
+
+1. Need about an hour to do both, but also speeding up