Ordinal number (encyclopediaofmath.org)>>464 https://encyclopediaofmath.org/wiki/Ordinal_number For instance, the ordinal number of the set N of all positive integers, ordered by the relation ≦, is ω. The ordinal number of the set consisting of 1 and numbers of the form 1-1/n where n∈N, ordered by the relation ≦, is ω+1. (引用終り)
有理数体Qで、順序数をQに埋め込めば簡単に理解できる 上記 The ordinal number of the set consisting of 1 and numbers of the form 1-1/n where n∈N で、n=1 から初めて 0,1/2,2/3,3/4,・・(n-1)/n,・・,1とできる さらに、2-1/n where n∈N を考える 1,1+1/2,1+2/3,1+3/4,・・1+(n-1)/n,・・,2 とできる