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+*View this file with results and syntax highlighting [here](https://mlochbaum.github.io/BQN/help/groupindices_group.html).*
+
+# Square Cup (`⊔`)
+    
+## `⊔ 𝕩`: Group Indices
+    
+Group the indices of the major cells of `𝕩` by their respective values.
+    
+## `𝕩` must consist of integers. Groups start from 0. 
+    
+           ⊔ 4‿5‿6‿6‿4‿7‿5
+
+           (↕8) ≍ ⊔ 4‿5‿6‿6‿4‿7‿5
+
+    
+    
+## `𝕨 ⊔ 𝕩`: Group
+    
+Group the major cells of `𝕩` by their respective indices in `𝕨`.
+    
+If an element corresponds to `¯1`, it is excluded from grouping.
+    
+An extra element can be added to the end of `𝕨` to specify length of the result.
+    
+           1‿0‿1‿2‿2‿3‿3  ⊔ 4‿5‿6‿6‿4‿7‿5
+
+           1‿0‿1‿¯1‿¯1‿3‿3  ⊔ 4‿5‿6‿6‿4‿7‿5
+
+           1‿0‿1‿¯1‿¯1‿3‿3‿10  ⊔ 4‿5‿6‿6‿4‿7‿5
+
+