I'm trying to understand the proof of theorem 1 in Stalling's Non-positively Curved Triangle of Groups. I have specific questions, but is there anywhere someone has written out the proof in more detail?
In the paper he eliminates from the graph of $(rf)^{-1} (T)$ curves of length less than two, but he needs to remove curves of \emph{weight} 2, did he mean weight? Or does this somehow imply we lose curves of that weight?