1. Ordering by divisibility in abstract algebras;Higman,1952
2. The theory of well quasi-ordering: A frequently discovered concept;Kruskal;J. Comput. Theory, Ser. A,1972
3. Combinatorics on words;Lothaire,1983
4. On well quasi-ordering transfinite sequences;Nash-Williams,1965
5. Partial well-ordering of sets of vectors;Rado;Mathematika,1954