A remark about the description of free products of groups
John Stallengs · Mathematical Proceedings of the Cambridge Philosophical Society · 1966
The free product A* B of groups A and B can be described in two ways. We can construct the set of reduced words in A and B. Define a binary operation on by concatenating two words and performing as many reductions as possible. Prove that is a group; the difficult step is the proof of associativity. Define A * B = .