u1 a 1b 2b 1 Gul Gu2 2 G21 G Ib L2 u2b Z1 ZI G11b G12bu1b 2 12 126 21a l2a 21b 22bJLu 2 b G1lb G12b ZI 21b z2 G11G12 ∠a Gelb G12b 2la 21b 22bNa + i1a + i2a u2a u1a Nb + i1b + i2b u1b u2b + u2 + u1 i1 i2 • • • • 2 1 u u 21 22 11 12 G G G G = 2 1 i i 2 1 i i = a a i i 2 1 + b b i i 2 1 a a u u 2 1 a a a a G G G G 21 22 11 12 = + b b u u 2 1 b b b b G G G G 21 22 11 12 a a a a G G G G 21 22 11 12 = + 2 1 u u b b b b G G G G 21 22 11 12 a a a a G G G G 21 22 11 12 = + b b b b G G G G 21 22 11 12 21 22 11 12 G G G G