Letter graphs and well-quasi-order by induced subgraphs.

Marko Petkovsek Letter graphs and well-quasi-order by induced subgraphs. 375-388 2002 244 Discrete Mathematics 1-3 http://dx.doi.org/10.1016/S0012-365X(01)00094-2 db/journals/dm/dm244.html#Petkovsek02