equation icon  | 4 d2S [g + h ±]| V~ ------V ~ ---------+IF----+---|| = - HabScd[g;x,y) - Kabcd[g;x, y) + iN abcd[g;x,y), -g(x) - g(y)dh ab(x)dh cd(y)|h±=h | (20) --------4-----------d2SIF[g-±]--|| abcd abcd V~ -----V ~ ------dh+ (x)dh -(y)|| = - H A [g;x,y) - iN [g;x,y), -g(x) - g(y) ab cd h±=h