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Libration will tend indeed to flatten radially across the horseshoe region the profile of any quantity conserved along a streamline. This is the case of the specific vorticity $B/\Sigma$ in an inviscid disk. Libration therefore tends to impose a decreasing profile of $\Sigma$ around corotation in an inviscid disk. Only in the special case of the shearing sheet, in which one neglects the radial variation of B, does libration tend to eliminate in-out surface density differences.

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