-- Case 4: parent is red, but uncle is black. Path to focus node is either L,R
-- or R,L
balance (Node nv nc nl nr, (Path R pv Red pl):(Path L gv gc u):path) =
  balance (Node pv Red pl nl, (Path L nv Red nr):(Path L gv gc u):path)
balance (Node nv nc nl nr, (Path R pv Red pl):(Path L gv gc u):path) =
  balance (Node pv Red pl nl, (Path L nv Red nr):(Path L gv gc u):path)
balance (Node nv nc nl nr, (Path R pv Red pl):(Path L gv gc u):path) =
  balance (Node pv Red pl nl, (Path L nv Red nr):(Path L gv gc u):path)