(this associates distinct numbers to "all" finite sets of natural numbers); then comparison of "k"-combinations can be done by comparing the associated binary numbers. In the example "C" and "C"' correspond to numbers 10010110012 = 60110 and 10100010112 = 65110, which again shows that "C" comes before "C"'. This number is not however the one one wants to represent the "k"-combination with, since many binary numbers have a number of raised bits different from "k"; one wants to find the relative position of "C" in the ordered list of (only) "k"-combinations.