add lab4 req

Labs/Lab4/lab4.md

@@ -4,4 +4,9 @@
 
 2. Inside this folder, there is a notebook `debug/self/main.ipynb`. Open it and fix the bugs. 
 
-3. Create a [binary search tree](./bst-groups) for use in P2. 
+3. Create a [binary search tree](./bst-groups) for use in P2. 
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+
+
+# Screenshot Requirement
+1. A screenshot showing the successfully debugged `main.ipynb`` notebook.
+2. A screenshot of your binary search tree implementation.
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