Nicolai, Hermann Quantum Gravity & Unified Theories, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
354831.pdf (Publisher version), 2MB
Englert, F., Nicolai, H., & Schellekens, A. (1986). Superstrings from 26 dimensions. Nuclear Physics B, 274(2), 315-348. doi:10.1016/0550-3213(86)90288-9.