Baratin, Aristide Quantum Gravity & Unified Theories, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
0910.1542v1.pdf (Preprint), 136KB
AIP1196_28.pdf (Any fulltext), 2MB
Baratin, A., & Wise, D. K. (2009). 2-Group Representations for Spin Foams. doi:10.1063/1.3284396.