Equation Icon  A = Ax (x)τ3dx + (A1(x )τ1 + A2 (x)τ2)dz + (A3 (x)τ1 + A4(x)τ2)dϕ (60 ) x -∂- 1 2 ∂-- 3 4 -∂- E = E (x)τ3∂x + (E (x)τ1 + E (x )τ2) ∂z + (E (x )τ1 + E (x)τ2)∂ϕ (61 )