matrix,matrix-multiplication,apl,dyalog

APL programmers should generally use Inner Product, as well as Outer Product, as much as possible. Is that correct? It is really up to the APL programmer and the task at hand, but if something makes APL code more concise and efficient, I don't see why a programmer wouldn't...

Ok, so I finally found (A B)←⊂[1 3]nl43[gr43[;4 5;] and am sadly disappointed by myself, as it never occured to me to re-think this bit before. Now that I answered that question myself, I assume there's not much room for refinement??? Hmm, there is a nested way to do this:...

evaluation,order-of-evaluation,apl,dyalog

You have nested functions. In both cases, the inner function simply returns its right and left argument. In the first case, the left argument to the inner function is the expression (○ 1×⍺), in the second case the left argument to the inner function is simply ⍺, or the unaltered...