Equation Icon  dx1-= − 1 − x − 3x + x2 − x x + x , (4.63 ) dN 3 2 1 1 3 4 dx2 x1x3 dN--= -m---− x2 (2x3 − 4 − x1 ) , (4.64 ) dx x x ---3= − -1-3-− 2x3(x3 − 2) , (4.65 ) dN m dx4- dN = − 2x3x4 + x1x4, (4.66 )