Grammatical coreference is such a kind of coreference in which it is possible to pinpoint the coreferred expression on the basis of grammatical rules.
The following types of grammatical coreference are distinguished:
coreference with reflexive pronouns (see Section 2.1, "Coreference with reflexive pronouns"),
coreference with relative elements (see Section 2.2, "Coreference with relative elements"),
coreference with verbal modifications that have a dual dependency (see Section 2.3, "Coreference with verbal modifications that have dual dependency"),
control (see Section 2.4, "Control"),
quasi-control (see Section 2.5, "Quasi-control"),
coreference in constructions with reciprocity (see Section 2.6, "Coreference in constructions with reciprocity").
It cannot not be said that one can always unambiguously determine what the coreferred expression is, just on the basis of grammatical rules. For example, in the sentence Přinesl jsem ti knihu o Boženě Němcové, kterou mám velice rád (=I brought you a book about BN, which I like a lot), the antecedent of the relative pronoun který (=which) can be Božena Němcová, as well as kniha (=book). However, there is no homonymy at the tectogrammatical level: it is clear from the tree which expression the dependent clause is dependent on.
Cases of grammatical coreference that do not respect the sentence boundaries are highly marked. For this reason, such occurrences are rather rare; nonetheless, they can be found in PDT, e.g.:
Na dnešní den byl oznámen začátek soudního řízení s nejznámějším a nejvlivnějším politikem Itálie za posledních padesát let, sedminásobným premiérem a symbolem mocenského režimu Křesťanské demokracie. Mužem, na němž se Italům líbila obratnost, chytrost, intelekt, lehký smysl pro humor, schopnost kompromisu. A kterého ztotožňovali tu s érou hmotného vzestupu, tu s hnilobnou stranokracií. (=Today, a lawsuit was started against the most powerful man in Italy....A man who was admired for his intellect, sense of humour... And which was identified with the era of material success...)
Grammatical coreference is represented with the help of the coref_gram.rf attribute (see Section 1, "Representing coreference in the tectogrammatical trees").