Light Element Settling in Main-Sequence Pop II Stars and the Primordial Lithium Abundance

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While theoretical computations of the lithium abundances in Pop II stars predict variations from star to star, the most recent observations confirm the existence of a "lithium plateau" with no abundance dispersion. This apparent paradox has to be faced and a solution has to be found before deriving the primordial lithium abundance. In any case lithium 7 has been depleted in these stars by at least 20 percent and lithium 6 by at least a factor 2, even in the hottest stars of the "plateau". Consequences for other elements are also discussed.