Specifically, I am looking for a proof that for squarefree $d\in\mathbb{N}\setminus\{ 1,3\}$, there exists some Kleinian $\Gamma$ and some $\alpha\in$Aut$(PSL(2,\mathbb{Z}))$, such that the Bianchi group $\Gamma\_d\cong \Gamma\*\_{\alpha}$. I have a reference that this proof appears in the article:


Charles Frohman and Benjamin Fine, "The amalgam structure of the Bianchi groups," 1986, *Compte Rendu RSC Mathematiques*, Volume 8, pp. 353-356.


But I cannot find access to this anywhere (at my university library, through Jstore, or anywhere else online). I did find an article on something very similar, by the same authors where they discuss amalgamated products instead. If I had to, I could probably go through that and alter the argument appropriately, but I expect it would take me more time than I can spare right now. Here is the info on the similar article in case that's useful:


Charles Frohman and Benjamin Fine, "Some Amalgam Structures for Bianchi Groups," 1988,
*Proceedings of the American Mathematical Society*, Vol. 102, No. 2, pp. 221-229 


From reading that and some similar things, I expect the approach would involve looking at finite-cover manifolds of the Bianchi groups, and finding incompressible embeddings of the totally real half-plane into them, but I'm lost on the details.



Frohman & Fine's proof about Bianchi groups as HNN extensions (or anyone else's)
The second reference listed in the question,


Charles Frohman and Benjamin Fine, "Some Amalgam Structures for Bianchi Groups," 1988, *Proceedings of the American Mathematical Society*, Vol. 102, No. 2, pp. 221-229,


does in fact include a proof of the statement in question. The article is available on [Jstor](http://www.jstor.org/discover/10.2307/2045866?uid=3739832&uid=2129&uid=2134&uid=2&uid=70&uid=4&uid=3739256&sid=21103368447467).


