Chen-Ning Yang and Robert L. Mills (1954). “Conservation of Isotopic Spin and Isotopic Gauge Invariance”. Physical Review 96: 191. doi : 10.1103/PhysRev.96.191 . T. D. Lee and Chen-Ning Yang (1956). “Question of Parity Conservation in Weak Interactions”. Physical Review 104: 254. doi : 10.1103/Phy...