Residual symmetry analysis and CRE integrability of the (3 + 1) -dimensional Burgers system Xi-Zhong Liu, Jun Yu, Zhi-Mei Lou and Xian-Min Qian Eur. Phys. J. Plus, 133 12 (2018) 503 Published online: 10 December 2018 DOI: 10.1140/epjp/i2018-12301-x