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+*View this file with results and syntax highlighting [here](https://mlochbaum.github.io/BQN/help/classify_indexof.html).*
+
+# Square Original Of (`⊐`)
+    
+## `⊐ 𝕩`: Classify  
+    
+First index of each major cell of `𝕩` in `𝕩`.
+    
+           ⊐ 5‿6‿2‿2‿5‿1
+
+           a ← 3‿3 ⥊ 0‿1‿2‿9‿0‿9‿0‿1‿2
+
+           ⊐ a
+
+    
+    
+## `𝕨 ⊐ 𝕩`: Index Of
+    
+First index of each major cell of `𝕩` in `𝕨`. Rank of `𝕩` must be at least cell rank of 𝕨`.
+    
+If a cell is not found in `𝕨`, that position will contain the length of `𝕨` (`≠𝕨`). 
+    
+           5‿6‿2‿2‿5‿1 ⊐ 5‿2‿1‿6
+
+           a ← 3‿3 ⥊ 0‿1‿2‿9‿0‿9‿0‿1‿2
+
+           a ⊐ ⟨9‿0‿9⟩
+
+
+