Nitrogen fixation is an important part of permaculture. Oregon State offers an online certificate in the subject.
https://pace.oregonstate.edu/catalog/permaculture-design-cer...
The amount of rubbish I've heard spouted by gardeners about what you should and shouldn't do is crazy.
And I'm not even talking about the more 'spiritual' side. Even seemingly mainstream type stuff like companion planting isn't internally consistent.
To bring it back to HN, I keep thinking there must be ways to model landscapes, and planting strategies to increase permaculture efficiency, although probably the antithesis of permaculture.
The issue seems to be putting plants together so they can support each other in close quarters, sounds like an optimisation problem to me, I've called it augmented permaculture before.
In fact, I thought about creating a "digital twin" for your edible landscape, and wrote about it here: https://automicrofarm.com/blog/2018/11/digital-twin.html