diff --git a/plan.txt b/plan.txt
index 5262c84..1eaf376 100644
--- a/plan.txt
+++ b/plan.txt
@@ -398,10 +398,12 @@ Know least one type of balanced binary tree (and know how it's implemented):
         - https://www.coursera.org/learn/data-structures/lecture/Qq5E0/avl-trees
         - https://www.coursera.org/learn/data-structures/lecture/PKEBC/avl-tree-implementation
         - https://www.coursera.org/learn/data-structures/lecture/22BgE/split-and-merge
-    - 2-3 Search Trees
-        - https://class.coursera.org/algs4partI-010/lecture/49
     - B-Trees:
+        - fun fact: B could stand for Boeing, Balanced, or Bayer (co-inventor)
+        - https://en.wikipedia.org/wiki/B-tree
         - https://class.coursera.org/algs4partI-010/lecture/51
+    - 2-3 (type of B-tree) Search Trees
+        - https://class.coursera.org/algs4partI-010/lecture/49
 
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