Hey, thanks for trying to reply substantively. You haven't understood what I was saying, which is fair enough because I didn't present it very clearly probably. The line where you start talking about something else is this: "So you’re saying I have a 1-dimensional, ordered set S, whose elements are real numbers". No, I'm not saying that. Firstly to define the question as Djikstra does: we're arging about, if I have a list L, and I write into my computer L[a, b], which elements of L are returned? My argument is kind of a physical metaphor, take the real number line as a physical axis (like you're doing physics), and take a load of toy trucks that each have length of 1 (I guess you choose your coordinate system to make the length 1) and put them down end to end. If I was a physicist, and I asked you to pick up 3 trucks starting at 0, and I was using real numbers and a vector I'd say it like this, pick up the trucks in the range [0, 3) on my axis.

Now if you choose 0 indexing + (closed, open) for your slicing, then a (python) programmer would say to another programmer, take the slice [0:3] to get the 3 trucks. So the slice numbers correspond perfectly to the vector description of the space that the items occupy. That's why in this slicing system taking L[a, b] then b-a = the number of items you get. Because it's matched perfectly with a real-number vector description of the space the items occupy on a real number line. All the other advantages like (I can describe an empty interval: [0:0]), I can describe taking the last element and it feels right [-1: 0] follow from this physical-space homomorphism. That last one: in a circular (modular?) space, walk left 1 and then come back right 1 and pick up the element you pass over. In 1-based: [0: 1] = the last element? I don't know if any languages do this but either you can't and that's sad or you can and it is incredibly counterintuitive.