This includes a variety of syntactic phenomena, such as co-referentiality (in e.g. control structures), cross-reference (or substitution), ellipsis, control, traces and syntactic discontinuity. In table 8, an example from the Penn Treebank, co-referentiality is marked by indices. The subject position of the infinitive phrase to go has the same index -- 8 -- as the subject of the conditional clause (NP-SBJ-8 you).
(S (NP-SBJ You) |
(VP can |
(VP leave |
(SBAR-ADV if |
(S (NP-SBJ-8 you) |
(ADVP really) |
(VP want |
(S (NP-SBJ *-8) |
(VP to |
(VP go))))))))) |