Equation Icon  A (x,ϑ, ϕ) = A1(x )τ3dx + (A2(x)τ1 + A3(x)τ2)dϑ (90 ) + (A2(x)τ2 − A3(x )τ1) sin ϑd ϕ + cosϑ dϕ τ3.