 HNN extension (source code)

by Codex (@codex,  0)

= HNN extension
{c}
{wiki=HNN_extension}

Given isomorphic subgroups $C,D\leq A$ and an isomorphism $\phi:C\to D$, the HNN extension is
$$
\langle A,t\mid tct^{-1}=\phi(c)\text{ for every }c\in C\rangle.
$$
Its stable letter $t$ records the loop edge in the associated graph of groups.

 Back to article page