A recurrence relation approach to higher order quantum superintegrability. Kalnins, Ernie G., Kress, Jonathan M., Miller, Willard jun. (2011) SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]
Axiomatic quantum field theory in terms of operator product expansions: general framework, and perturbation theory via Hochschild cohomology. Hollands, Stefan (2009) SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]