bug: compose edge case

https://code.jsoftware.com/wiki/Vocabulary/ampv


```
   (i.5 2) ,&<"_1 i.5 5
+---+--------------+
|0 1|0 1 2 3 4     |
+---+--------------+
|2 3|5 6 7 8 9     |
+---+--------------+
|4 5|10 11 12 13 14|
+---+--------------+
|6 7|15 16 17 18 19|
+---+--------------+
|8 9|20 21 22 23 24|
+---+--------------+
   
```