Top: variation in the radial differential rotation with mass fraction of hydrogen in the core. The value in the envelope is held fixed at 0.7, while that of the core is decreased as would be the case when the stars evolve. The angular velocity is half of the break-up: Ω_eq = 0.5   Ω_k. Middle: same as top but for the surface differential rotation. Bottom: the ratio of the angular velocity at the pole of the core and at the bottom of the envelope on the rotation axis.