It should be noted here that our focus is on improving parsing performance using a single underlying grammar class, which is somewhat orthogonal to the issue of parser combination, that has been studied elsewhere in the literature (Sagae and Lavie, 2006;Fossum and Knight, 2009;Zhang et al., 2009).
to that line of work, we also do not restrict ourselves to working with kbest output, but work directly with a packed forest representation of the posteriors, much in the spirit of Huang (2008), except that we work with several forests rather than rescoring a single one.