The relationship between the depletions of ^ { 6 } Li and ^ { 7 } Li is studied for two models of lithium burning , below the convective zone .
The parameters of the depletion models are submitted to the constraint that the slope of the ^ { 7 } Li theoretical depletion curve agrees with the slope of the observed depletion curve , for cool subdwarfs .
Other less restrictive models are also considered . In all cases , a ^ { 6 } Li depletion less than 0.5 dex implies a ^ { 7 } Li depletion less than 0.1 dex .
With the constraint on the slope of the ^ { 7 } Li curve , the depletion of ^ { 7 } Li for the same depletion of ^ { 6 } Li is below 0.05 dex .

The still unsolved problem for the true ^ { 7 } Li abundance in subdwarfs is the possible influence of temperature inhomogeneities , raised by Kurucz , subsequently shown to be small in the solar case , but not yet computed with the inclusion of departure from LTE for metal-poor stars .