Let $F$ and $H$ be two free groups, where $F = \langle a,b\rangle$ and $H = \langle aa,bb,aba,baab, babab\rangle$. Let $N(H)$ be the normalizer of $H$ in $F$.
How can I compute $N(H)/H$?
In general, given a presentation of a group, is there a way to find its normalizer?