1. Riemann, B.: On the hypotheses which lie at the bases of geometry. translated by William K.Clifford, Nature VIII 183, 184, 14–17
2. Grosse H. and Wulkenhaar R. (2006). Noncommutative QFT and renormalization. Fortschr. Phys. 54: 116
3. Letter of Heisenberg to Peierls: In: Wolfgang Pauli (ed.) Scientific Correspondence, vol. 2, 15. Karl von Meyenn (ed.) Springer, Heidelberg (1985)
4. Snyder H.S. (1947). Quantized spacetime. Phys. Rev. 71: 38
5. Letter of Pauli to Bohr (1947): In: Wolfgang Pauli (ed.) Scientific Correspondence, vol. 2, 414, Karl von Meyenn (ed.) Springer, Heidelberg (1985)