@rabbitgrowth yes, I'd tried with QuadEqual from Vision but got different results then the examples so confused how you'd expected to apply your solution

@Silas (≢¨0 1⌸)1 1⍉∘.> seems to work.

{⎕IO←0 ⋄ ⍵[i]×1-⍨⊖i←3|-∘.+⍨⍳3}

⍵[i]

anyone know why you can use i to index w?

i is a 3x3 matrix?

@1234 Odd question, imo. APL is an array language, so it allows arrays as indexers. The result of an indexing operation on a vector has the shape of the indexer, each element of the indexer selecting a part of of the indexee.

@rabbitgrowth right, thanks! Figured there'd be some pre processing somehow :)

in my quest to document all glyphs ever used in any dialect I'm coming across some weird primitives

like monadic ∘. in NARS, "function table"

basically {⊃∘.⍺⍺/⍳¨⍵}

so like ∘.× 5 5 makes the 5x5 multiplication table

I wonder why this was ever included

kinda feels like they noticed there was no monad ∘. so they went with something random