Proof-reading session on traversing relations

[pietercolpaert]

https://treecg.github.io/specification/#relationsubclasses

There are questions on data types and full list of relations that need to be formally specified in each subsection

All datatypes in https://www.w3.org/TR/rdf-interfaces/#literals should be discussed

[pietercolpaert]

Related: What if an equalToRelation on an xsd:date is compared to an xsd:dateTime? We need to specify that the dateTime needs to be casted to the xsd:date