After finding formal definitions in various texts (see, eg, Witten, _Notes On Some Entanglement Properties Of Quantum Field Theory_, Rev. Mod. Phys. 90, 45003 (2018), doi:[10.1103/RevModPhys.90.045003](https://doi.org/10.1103/RevModPhys.90.045003) arXiv:[1803.04993][1]), I have ($I$) not been able to obtain a good intuition for them and ($II_1$) have not seen anyone relate such factors to more commonly understood Hilbert spaces such as $L^2(\mathbb R)$. This is very likely for good reason, but it would be nice to have these ideas come down from the clouds so that one can present them to non-mathematicians and (maybe this is too ambitious) laypeople.


  [1]: https://arxiv.org/abs/1803.04993