Naming sets where the elements are a combination of indices

Very clear. Thank you. The examples in the link you shared are interesting as well. As a follow-up question to the example in proj.mos: I understand the difference in the enumeration results in the 4 loops demonstrated. If you use exists, then the difference is that "range" will return ordered tuples, while "set of integer" will report them in the order they appear. So should I expect that "set of integer" will be faster because there is no sorting? Is the difference noticeable? Which is recommended for indexing integers: range or set of integer? Thanks for your perspective.