Quibble := proc( los )
  uses  StringTools;
  Fence( proc()
        if los = [] then
          ""
        elif numelems( los ) = 1 then
          los[ 1 ]
        else
          cat( Join( los[ 1 .. -2 ], ", " ), " and ", los[ -1 ] )
        end if
  end(), "{", "}" )
end proc: