Ronald Reagan takes oath as 40th president (Jan. 20). U.S.-Iran agreement frees 52 hostages held in Tehran since 1979 (Jan. 20); hostages welcomed back in U.S. (Jan. 25). President Reagan wounded by gunman, with press secretary and two law-enforcement officers (March 30). Pope John Paul II wounded by gunman (May 14). Reagan nominates Judge Sandra Day O'Connor, 51, of Arizona, as first woman on Supreme Court (July 7). More than 110 die in collapse of aerial walkways in lobby of Hyatt Regency Hotel in Kansas City; 188 injured (July 18). Air controllers strike, disrupting flights (Aug. 3); government dismisses strikers (Aug. 11).AIDS is first identified.