%0 Journal Article %A D'Alessandro, Flavio %A Varricchio, Stefano %T Well quasi-orders, unavoidable sets, and derivation systems %J RAIRO. Theoretical Informatics and Applications %D 2006 %P 407-426 %V 40 %N 3 %I EDP-Sciences %U https://www.numdam.org/articles/10.1051/ita:2006019/ %R 10.1051/ita:2006019 %G en %F ITA_2006__40_3_407_0