Stefan Arnborg Andrzej Proskurowski Detlef Seese Monadic Second Order Logic, Tree Automata and Forbidden Minors. 1-16 1990 conf/csl/1990 CSL db/conf/csl/csl90.html#ArnborgPS90 http://dx.doi.org/10.1007/3-540-54487-9_49