Comment by geocar

> and what is obvious to one can be surprising to someone else.

That is how obvious things work. If you were not surprised that a[i:j] and :[a;i;j] are the same (: a i j) then it is because it was obvious to you, and now that you have had it pointed it out to you, you were able to show all of the different other variants of this thing without even being prompted to, so I think you understand the answer to your question now.