Detecting Matroid Minors
Paul D. Seymour, Philippa Walton · Journal of the London Mathematical Society · 1981
When % is a collection of matroids, the question whether M has a minor in % can be easy or hard, depending on the choice of < 6. More precisely, the number of demands made on an "independence oracle" to decide the question sometimes can be bounded above by a polynomial in \\E(M)\\, and sometimes it cannot. We study this, and in particular classify each singleton % as easy or hard.