Discussion of the 8th study group can go here. Overview
[ <<< session 7 | session 9 >>>]
This is a wiki post - feel free to edit to add links from the lesson or other useful info.
Many APLers frown on Bracket Axis (and Bracket Indexing) as anomalous syntax, and as you found, there being no general rule (so you cannot have intuition about what Bracket Axis does for any particular function) and it (therefore) cannot be applied to user-defined functions.
The modern alternative is using the Rank Operator (⍤), often together with (dyadic) transpose (⍉), which is completely general, so one can learn a single pattern and have it apply to all functions. Very few constructs remain where Bracket Axis provides value, and we are working on making those even fewer.
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Is there a general way to guess what the next session will cover? Sort of want to read a little bit ahead so I can contribute more to the conversation.
We could decide here on the forum what we’ll aim to cover next time. @Moody listed some things she’d like to see covered yesterday – we could aim to look at those?.. We should probably at least cover Transpose tomorrow
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Okay I will be taking a look at ⌸, ⊆,⊂, ↑,↓, @, Reduce N-Wise, and ⍉ then. 
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