On the Tits alternative for some generalized triangle groups

One says that the Tits alternative holds for a finitely generated group $\Gamma$ if $\Gamma$ contains either a non abelian free subgroup or a solvable subgroup of finite index. Rosenberger states the conjecture that the Tits alternative holds for generalized triangle groups $T(k,l,m,R)=\langle a,b; a^k=b^l=R^m(a,b)=1\rangle$. In the paper Rosenberger's conjecture is proved for groups $T(2,l,2,R)$ with $l=6,12,30,60$ and some special groups $T(3,4,2,R)$.