  A recent advance in monolingual dependency parsing is the idea of a treebank
embedding vector, which allows all treebanks for a particular language to be
used as training data while at the same time allowing the model to prefer
training data from one treebank over others and to select the preferred
treebank at test time. We build on this idea by 1) introducing a method to
predict a treebank vector for sentences that do not come from a treebank used
in training, and 2) exploring what happens when we move away from predefined
treebank embedding vectors during test time and instead devise tailored
interpolations. We show that 1) there are interpolated vectors that are
superior to the predefined ones, and 2) treebank vectors can be predicted with
sufficient accuracy, for nine out of ten test languages, to match the
performance of an oracle approach that knows the most suitable predefined
treebank embedding for the test set.
