This lecture is part of a series which gives an expanded version of the Vinberg lecture on "Vinberg's algorithm and Kac-Moody algebras". This video is part 3 and describes how to associate Lie algebras to some hyperbolic reflection groups.
The original version of the Vinberg lecture is here:
https://amathr.org/Borcherds-vinberg/
For the other lectures see
• Vinberg lecture