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This is an exposition in three screencasts of the topological proof of Grushko's Theorem
due to Stallings. I made this several years ago when teaching a similar course.
21.1: Stallings topological proof of Grushkos theorem I: Statement and idea
21.2: Stallings topological proof of Grushkos theorem II : Binding ties
21.3: Stallings topological proof of Grushkos theorem III : Construction of Binding ties