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Talk:Ping-pong lemma

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This is an old revision of this page, as edited by Nomeata (talk | contribs) at 17:22, 15 February 2022. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

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Why “infinite order”?

Section “The Ping-pong lemma for cyclic subgroups” has some requirements, such as that the a_i have infinite order. Sure, they must have infinite order in the end, but is it really a precondition? The Isabelle proof at https://afp.theoremproving.org/entries/free-groups/theories/#PingPongLemma (which unfortunately doesn't cite any sources) doesn’t have such a requirement.

The precondition was added in this anonymous change: https://en.wikipedia.org/w/index.php?title=Ping-pong_lemma&diff=842423303&oldid=826906226

Also, is there a source for this section that could be cited here? Nomeata (talk) 17:21, 15 February 2022 (UTC)[reply]

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