Title: Are crossing dependencies really scarce?,
Abstract: The syntactic structure of a sentence can be modelled as a tree, where
vertices correspond to words and edges indicate syntactic dependencies. It has
been claimed recurrently that the number of edge crossings in real sentences is
small. However, a baseline or null hypothesis has been lacking. Here we
quantify the amount of crossings of real sentences and compare it to the
predictions of a series of baselines. We conclude that crossings are really
scarce in real sentences. Their scarcity is unexpected by the hubiness of the
trees. Indeed, real sentences are close to linear trees, where the potential
number of crossings is maximized.