1. Finkelstein, D., Jauch, J.M., Schiminovich, S., Speiser, D.: Foundations of quaternion quantum mechanics. J. Math. Phys. 3, 207 (1962)
2. Aaronson, S.: Is quantum mechanics an island in theoryspace? In: Khrennikov, A. (ed.) Proceedings of the Växjö Conference “Quantum Theory: Reconsideration of Foundations”. Växjö University Press, Växjö (2004)
3. Hardy, L.: Disentangling nonlocality and teleportation. arXiv:quant-ph/9906123v1
4. Spekkens, R.W.: Evidence for the epistemic view of quantum states: a toy theory. Phys. Rev. A 75, 032110 (2007)
5. Hughes, G., Cresswell, M.: A New Introduction to Modal Logic. Routledge, London (1996)