# Sh:745

- Nešetřil, J., & Shelah, S. (2003).
*On the order of countable graphs*. European J. Combin.,**24**(6), 649–663. arXiv: math/0404319 DOI: 10.1016/S0195-6698(03)00064-7 MR: 1995579 -
Abstract:

A set of graphs is said to be*independent*if there is no homomorphism between distinct graphs from the set. We consider the existence problems related to the independent sets of countable graphs. While the maximal size of an independent set of countable graphs is 2^\omega the*On Line*problem of extending an independent set to a larger independent set is much harder. We prove here that singletons can be extended (“partnership theorem”). While this is the best possible in general, we give structural conditions which guarantee independent extensions of larger independent sets. This is related to universal graphs, rigid graphs and to the density problem for countable graphs. - published version (15p)

Bib entry

@article{Sh:745, author = {Ne{\v{s}}et{\v{r}}il, Jaroslav and Shelah, Saharon}, title = {{On the order of countable graphs}}, journal = {European J. Combin.}, fjournal = {European Journal of Combinatorics}, volume = {24}, number = {6}, year = {2003}, pages = {649--663}, issn = {0195-6698}, mrnumber = {1995579}, mrclass = {03C50 (03C98 05C60)}, doi = {10.1016/S0195-6698(03)00064-7}, note = {\href{https://arxiv.org/abs/math/0404319}{arXiv: math/0404319}}, arxiv_number = {math/0404319} }