7 As a general rule, non-projective arcs were only al lowed if no other, projective head could be found for a given word.
linguistic knowledge suggests that non-projective arcs should be particu larly likely in connection with verb-chain-depen dencies, where subjects attach to the finite verb, but objects to the non-finite verb, which can create crossing arcs in the case of object fronting, chain inversion etc.