@Adám Oh, I see now. I don’t know if I had a cleverer idea before or just had it wrong, but my intent was something like this: ⍳⍥((((⊂⊢⌷⍨∘⊂⍋)⍤⍳⍨⌷⊢)⊂⍤,⍤0(∊{⊂⍳≢⍵}⌸)⍤⍳⍨)⌷⍨∘⊂(⍋∘⍋)⍤⍳⍨)

@hyper-neutrino Can you give chat.stackexchange.com/users/553557/user113661 access?

… and chat.stackexchange.com/users/553855/user19604705