@article{Conway2002TheON,
title={The Orbifold Notation for Two-Dimensional Groups},
author={J. H. Conway and D. Huson},
journal={Structural Chemistry},
year={2002},
volume={13},
pages={247-257}
}

This paper gives a detailed introduction to the orbifold notation for two-dimensional (2-D) symmetry groups. It discusses the correspondence between properties of orbifolds and symmetries in the original surface. The problem of determining a group in situ is addressed. Elementary proofs of the classification of the Euclidean and spherical 2-D symmetry groups are presented.