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# Total ordering of sets of fixed size

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Problem Detail:

I'm curious if there is a name for this way of ordering finite sets of natural numbers (shown here for the case 3 elements, but can be extended to any number of them):

``{0, 1, 2} < {0, 1, 3}           < {0, 2, 3}           < {1, 2, 3}           < {0, 1, 4}           < {0, 2, 4}           < {1, 2, 4}           < {0, 3, 4}           < {1, 3, 4}           < {2, 3, 4}           < {0, 1, 5}           < ... ``

The sets are generated recursively: increase the highest number and reset all the other elements to the lowest possible numbers, then apply this algorithm recursively to the remaining numbers.

The position within this ordering is given by:

``C(x[1], 1) + C(x[2], 2) + C(x[3], 3) + ... ``

where `x[i]` is the `i`-th element in the sorted set and `C(n, k)` is the binomial coefficient.

Does anyone know of a name for this kind of total ordering? Furthermore, what other common ways are there to order sets containing a fixed number of totally ordered elements?

This is just lexicographical order, but left to right (not right to left as usual).