Theisen, Stefan Quantum Gravity & Unified Theories, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
379521.pdf (Publisher version), 2MB
Lüst, D., & Theisen, S. (1988). Four-dimensional heterotic strings-orbifolds and covariant lattices. Nuclear Physics B, 302(3), 499-524. doi:10.1016/0550-3213(88)90212-X.