Hyperbolic triangle group
= Hyperbolic triangle group
{title2=$\Delta(p,q,r)$}
{wiki=Triangle_group}
When $1/p+1/q+1/r<1$, the orientation-preserving hyperbolic triangle group has presentation
$$
\Delta(p,q,r)=\langle a,b,c\mid a^p=b^q=c^r=abc=1\rangle
$$
and is a non-elementary Fuchsian group.