2 basic regular quotient singularity types and
4 irregular quotient singularity types
| Singularity type | Index |
|---|---|
| [2] | 1 |
| [2, [2], [2, 2], [2, 2]] | 1 |
| [2, [2], [2, 2], [2, 2, 2]] | 1 |
| [2, [2], [2, 2], [2, 2, 2, 2]] | 1 |
| Basic singularity type | Second singularity type | Third singularity type | Index |
|---|---|---|---|
| [2, 2] | [2, 2, 2] | [2, 2, 2, 2] | 1 |
| [2, [2], [2], [2]] | [2, [2], [2], [2, 2]] | [2, [2], [2], [2, 2, 2]] | 1 |
Reference: R. Blache, "Two aspects of log terminal surface singularities", Abh. Math. Sem. Univ. Hamburg 64 (1994), 59-87