So I've been trying to do the 19th exercise, the top-left to bottom-right line one, and while trying to do something clever with ¦ (having hit 8 bytes with two separate more straightforward approaches) I realized that I don't really know how to use it at all

(got one of them down to 7 actually, but still two bytes over par)

...6 now

and the thing I was going to do with ¦ would absolutely not help but that quick still confuses me

and now I've come up with a completely different 6-byter

with trailing spaces

it's actually 5 bytes with trailing spaces

and somehow all that progress was inspired by being confused by ¦

applying the same idea I've hit 7 bytes on 21 and 22 (checkerboards) and... it seems like they should only need 6

similarly I got 8 on 20 (the X one)

@UnrelatedString It's not too bad of a quick to get the hang of. Basically, it takes an atom, a list and a list of indices, and applies the atom to the values in the list at those indices

So H[1,2,3]¦ would halve the first three elements of the input list

Try it online!