The mayor of Beijing has, Musk said he believed, an environmental engineering degree, and the deputy mayor has a physics degree.

Judge as of 7 September 2018. Identify who was Mayor of Beijing on that date and the deputy mayors then in office. True: the mayor holds a degree in environmental engineering (any level: bachelor's, master's or doctorate), and at least one sitting deputy mayor holds a degree in physics. Mostly true: both parts hold in substance, but with a small slip in a detail, for example the mayor's degree is in a closely named environmental engineering or environmental science field, or the physics-trained person was a deputy mayor in a closely related role. Mixed: one of the two parts holds and the other does not. Mostly false: neither part holds exactly, but one rests on something real, for example a related technical degree that is not environmental engineering or physics. False: the mayor has no environmental engineering degree and no deputy mayor in office has a physics degree.

Set before the research began.

1. E1 Beijing elects new leadership | english.scio.gov.cn State Council Information Office of China (SCIO) · 31 January 2018

   “Chen Jining was elected as the mayor of the Beijing Municipal People's Government. Zhang Gong, Yin Hejun, Zhang Jiandong, Sui Zhenjiang, Wang Ning, Yin Yong, Lu Yan, Yang Bin and Wang Hong were elected as vice mayors.”

2. E2 China names new science ministry chief to help lead hi-tech self-reliance drive South China Morning Post · 9 October 2023

   “Born in the northwestern province of Shanxi, Yin earned a master’s degree in radiophysics from Xidian University in 1989 and worked at Taiyuan University of Technology for three years.”

3. E3 China names new science ministry chief to help lead hi-tech self-reliance drive South China Morning Post · 9 October 2023

   “In 2017, Yin was appointed Beijing’s vice-mayor, earning praise from his boss, then Beijing party secretary Cai Qi, for his familiarity with scientific research and technology management.”

4. E4 Mayor of Beijing - Wikipedia Wikipedia

   “Chen Jining (born 1964) | 30 January 2018 (acting from 27 May 2017) | 28 October 2022”

5. E5 新一届北京市人大常委会市政府领导选出(名单) Sina News (reprinting Beijing Daily, 北京日报) · 30 January 2018

   “研究生毕业（英国帝国理工学院环境系统分析专业），工学博士，教授。”

6. E6 Politics of Beijing - Wikipedia Wikipedia

   “Chen Jining (born 1964) | 30 January 2018 (acting from 27 May 2017) | 28 October 2022”

7. E7 新一届北京市人大常委会市政府领导选出(名单) Sina News (reprinting Beijing Daily, 北京日报) · 30 January 2018

   “阴和俊，男，汉族，1963年1月生，山西古交人，1983年6月加入中共，1983年9月参加工作，研究生毕业（中国科学院电子学研究所电磁场与微波技术专业），工学博士，研究员。”

8. E8 新一届北京市人大常委会市政府领导选出(名单) Sina News (reprinting Beijing Daily, 北京日报) · 30 January 2018

   “市人民政府市长陈吉宁，副市长张工、阴和俊、张建东、隋振江、王宁、殷勇、卢彦、杨斌、王红；”

The evidence shows Chen Jining was mayor on the date [E1, E4]. It also shows that vice-mayor Yin Hejun, elected in January 2018, holds a master's in radiophysics [E1, E2, E7]. The only quoted degree profile for the mayor [E5] does not name the person it describes, so the evidence does not settle whether the mayor holds an environmental engineering degree.