  Spin-orbit interaction lifts accidental band degeneracy. The geometric phase
gamma(C)=pi for circuits surrounding a line of such degeneracy cannot survive
completely unchanged. The change depends on how the spin is fixed during
adiabatic evolution. For spin fixed along the internal spin-orbit field,
gamma(C) decreases to zero as the circuit collapses around the line of lifted
degeneracy. For spin fixed along a perpendicular axis, the conical intersection
persists and gamma(C)=pi is unchanged.
