> < ^ From:

> < ^ Subject:

Dear friends, Since noone has yet answered this question, I volunteer. If one

kills the generators of the "base group", the quotient is isomorphic to the

infinite cyclic group with presentation <t| >. So the stable letter t maps

to a generator of Z, and thus has infinite order in the HNN group.

(Geometrically, the "torus" collapses onto the "core S^1".)

Best regards, Michael Falk.

>

> Dear Gap-Forum,

>

> I have a conceptual question concerning "HNN extensions".

>

> In the book

>

> B. Chandler / W. Magnus, "The History of Combinatorial Group Theory" (1982)

>

> on page 111, the definition of the HNN extension is given. It is followed

> by the remark: "In particular, t (the "stable letter") is always of infinite

> order in H (the extended group)."

>

> Is this remark really correct - and if, then why ?

>

> Thank you!

> --Toni

>

>

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