1 Lisa Ferdinado, “U.S., Russia Sign Memorandum on Air Safety in Syria,” U.S. Department of Defense News, October 20, 2015, accessed April 24, 2018, https://www.defense.gov/News/Article/Article/624964/us-russia-sign-memorandum-on-air-safety-in-syria/.

2 “Turkey’s downing of Russian warplane–what we know,” BBC News, December 01, 2015, accessed April 24, 2018, http://www.bbc.com/news/world-middle-east-34912581.