In the section about ?, i think you have forgotten about this functionality of ?:

 ?2  /monadic integer scalar
0.3999661641903345 0.6017000472937657
 ?5
0.5879972736671595 0.17700198635766617 0.9307749326543255 0.25312536316484247 0.21150427354311319
 ?1
,0.2984588148454079

Hi, a simple typo (missing s) in

We’ll use that to make variable assignments visible in output occaionally:
                                                                 ^^^

Keep up the great work, Stefan!

In the indexing section,
m[(2 2;1 1)] / note: this is NOT indexing at depth!

It might be good to provide a combination of both indexing with a vector and also nesting, and a small explanation of how to interpret it.

This seemed to clear it a little bit for me (I'm still on the learning process)

m[(0 1;1 2;2 1)]
((0 1 2;3 4 5)
 (3 4 5;6 7 8)
 (6 7 8;3 4 5))

m[(0 1;1 2;2 1);1]
(3 4 5
 6 7 8
 3 4 5)

Thanks a lot for your apl and k learning resources!