IN MUSIC, Operatically named Gilbert O’Sullivan (right) tops the singles chart with ”Alone Again (Naturally),” a melancholy ditty that some say deals with the death of his parents. In 1991, a federal judge will bar rap star Biz Markie from sampling the single. ON BROADWAY, Art Carney and Barbara Barrie play frazzled New Yorkers dealing with midlife hardships in Neil Simon’s The Prisoner of Second Avenue. In 1975, the play will become a movie starring Jack Lemmon and Anne Bancroft. IN BOOKSTORES, Richard Bach’s New Age tome Jonathan Livingston Seagull perches atop the fiction chart. In 1973, it will be made into a film featuring songs by Neil Diamond. AND IN THE NEWS, delegates to the Republican National Convention gather in Miami Beach to nominate incumbent President Richard Nixon.