The green lines in the diagram below are the 4 relations of the Trinity:
1. paternity (the relation of the Father to the Son)
2. filiation (the relation of the Son to the Father)
3. spiration of the Holy Spirit (the relation of the Father and the Son in respect to the Holy Spirit)
4. procession of the Holy Spirit (the relation of the Holy Spirit in respect to the Father and the Son)


I welcome any criticisms, comments, or suggestions about this diagram. I made it because I've never seen one of these sort of diagrams that includes the relations.

(I'm learning TikZ, which is very powerful for making diagrams like this one. See its code here. The PGF/TikZ manual is very good and well-docuмented. Its code examples are heavily cross-linked, so you can click on any command, and it'll bring you to the page that describes that command.)