This book looks like it may be a nice complement to these CAT notes: https://www2.math.upenn.edu/~ghrist/notes.html https://www2.math.upenn.edu/~ghrist/notes.h

This book looks like it may be a nice complement to these CAT notes: https://www2.math.upenn.edu/~ghrist/notes.html https://www2.math.upenn.edu/~ghrist/notes.html (I haven't gone through either.)