In this recent preprint on Paul Seymour's webpage: http://web.math.princeton.edu/~pds/papers/pure5/paper.pdf (not on ArXiv nor published yet)
Claimed to be solved
In this recent preprint on Paul Seymour's webpage: http://web.math.princeton.edu/~pds/papers/pure5/paper.pdf (not on ArXiv nor published yet)