Equation Icon  ( ) | 0 1 0 | gab = || 1 g11 g1A || , (2.9 ) ( ) 0 g1A gAB g11 = 2(U − ωω¯), g1A = XA − (ω¯ξA + ωξ¯A ), AB A B B A g = − (ξ ξ¯ + ξ ¯ξ ).