In which TV series is Vinnie Barbarino a main character?

Who played Laura Ingalls in 'Little House on the Prairie'? In which TV series is Laura Ingalls a main character? Who played George Jefferson in 'The Jeffersons'? Who played Vinnie Barbarino in 'Welcome Back, Kotter'? Who played Jack Tripper in 'Three's Company'? Who played Chrissy Snow in 'Three's Company'? In which TV series is Chrissy Snow a main character? Who played Mork in 'Mork & Mindy'?