Gardiner, S., & Billam, T. (2013). Number-conserving approaches for atomic Bose-Einstein condensates: an overview. In N. Proukakis, S. Gardiner, M. Davis, & M. Szymanska (Eds.), Quantum Gases: Finite Temperature and Non-Equilibrium Dynamics (133-145). Imperial College Press. https://doi.org/10.1142/9781848168121_0008