> - Establishing relationships between entities in a body of text. E.g. we could build a fact-graph from sentences like "Burning coal increases CO2", and "CO2 increase induces global warming". Useful also in medical literature where there are millions of pathways.

That's a simple example because with 'CO2' you at least have the same string that can serve as a keyword connecting those two facts. Usually in natural language we make frequent use of anaphora to refer to people, objects and concepts previously mentioned in the text by name.

Anaphora resolution is one of the really hard problems not only in NLP but in linguistics in general. The most simple anaphoric device in languages like English is pronouns and even with those it can be quite difficult to determine what a 'he' or 'she' refers to in context.