Equation Icon  sum L D2 -loop = - sl .sl+2 + 4sl .sl+1- 3 .1 i=1 sum L D = - s .s + (s .s )(s .s )- (s .s )(s .s ) 3- loop l l+3 l l+2 l+1 l+3 l l+3 l+1 l+2 i=1 +10 sl .sl+2 - 29 sl .sl+1 + 20 .1 .