Who played Vinnie Barbarino in 'Welcome Back, Kotter'?

In which TV series is Charles Ingalls 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'? In which TV series is Vinnie Barbarino a main character? 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?