Editing Link grammar (section)

===Planarity===
The parsing algorithm also requires that the final graph is a [[planar graph]], i.e. that no links cross.<ref name="intro"/> This constraint is based on empirical psycho-linguistic evidence that, indeed, for most languages, in nearly all situations, dependency links really do not cross.<ref>{{cite conference |author=J. Havelka |year=2007 |title=Beyond projectivity: multilingual evaluation of constraints and measures on non-projective structures |conference=Proceedings of the 45th Annual Meeting of the Association of Computational Linguistics |pages=608–615 |place=Prague, Czech Republic |publisher=Association for Computational Linguistics}}</ref><ref>{{cite journal |author=R. Ferrer i Cancho |title=Why do syntactic links not cross? |journal=EPL |volume=76 |number=6 |year=2006 |pages=1228–1234|doi=10.1209/epl/i2006-10406-0 |bibcode=2006EL.....76.1228C |hdl=2117/180367 |hdl-access=free }}</ref> There are rare exceptions, e.g. in Finnish, and even in English; they can be parsed by link-grammar only by introducing more complex and selective connector types to capture these situations.