>>131,133
Only if you're directly working with it and not through some other interface. It of course makes sense when you are the one writing the implementation. >>133
In set theory, when someone wants order in an unordered set they can just make a set of ordered pairs, in the sense:
ordered {a,b,c} - would be {(1,a),(2,b),(3,c)}, of course this isn't that much different from just defining a function f:{1,2,3}->{a,b,c}.