Rosver, are you asking about normal “Links” the umbilical cords, or the demon to Abyss link.
The normal links are pretty well understood in all the various forms of magic. I have several articles on them that will make their way out.
One big problem I have is that I’ve lost a lot of my old writings (or stored them somewhere I can’t find).
The original stuff was mostly in AmiPro and later maybe some Word Pro…so just extracting the text is a bit tedious.
One big loss was a thing called the Wizard’s Appendix. I haven’t been able to find an electronic copy, yet. However, I did find a printed copy of it that I scanned to PDF last night. I’m not sure how complete it is.
That has stuff on Links, Mana Pools, Arcane Devices, more on Demons (from a Wizards point of view).
As far as the link to the Abyss, that may or may not make it’s way out. Probably will by the end. It’s tied to the nature of the Abyss and that other discussion in the forums about the Abyss not like other planes and the river Styx.