I understand that group cohomology description for symmetry protected topological phases (SPT) comes from discrete nonlinear sigma models. A tutorial on this can be found in the excellent lectures by Prof Xiao-Gang Wen:
https://www.youtube.com/watch?v=OOIihbejEDQ&t=20s.
I also understand the cohomology group also corresponds to the t'Hooft anomaly of the symmetry on the boundary. How should I understand this? What are the pedagogical papers on this issue?
