Hyperbolic triangle group
= Hyperbolic triangle group
{title2=$\Delta(p,q,r)$}
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.
This is the orientation-preserving hyperbolic member of the broader <triangle group> construction.