Can anyone recommend me references dealing with involutive systems of vector fields?
I'm taking a course which is using the book An Introduction to Involutive Structures (F. Berhanu, J. Hounie, P. Cordaro), it's a survey of the last 25 years in the subject, however I find it hard to follow.
There is also the book Hypo-analytic structures (F. Treves) however I don't have access to it and I can't buy it too.
If someone could recommend me other books (lecture notes...) apart from the two above I would appreciate.
Thanks
