> Also, the domain should define how to compare objects and could provide
> details about whether the set is finite, countable or uncountable.

Sounds like a role "Domain" that provides methods (off the top of my head)-

ordering - returns Nil if the domain is unordered, or a method
implementing "cmp" if it is ordered

succ, pred- returns Nil if the domain is uncountable, or method
implementing "next item", "prior item" if countable.

count - returns Inf if it's an infinite domain, or count of objects if
finite. What if counting is an expensive operation? perhaps there
should also be an "is_infinite" method that returns true or false.

Then the .. operator can accept anything that does Domain where
ordering is non-Nil, and the ... operator can add the condition that
succ/pred are non-Nil.

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