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))))))))) |