  We present FLAMES/GIRAFFE spectroscopy obtained at the Very Large Telescope
(VLT). Using these observations we have been able for the first time to observe
the Li I doublet in the Main Sequence stars of a Globular Cluster. We also
observed Li in a sample of Sub-Giant stars of the same B-V colour. Our final
sample is composed of 84 SG stars and 79 MS stars. In spite of the fact that SG
and MS span the same temperature range we find that the equivalent widths of
the Li I doublet in SG stars are systematically larger than those in MS stars,
suggesting a higher Li content among SG stars. This is confirmed by our
quantitative analysis which makes use of both 1D and 3D model atmospheres. We
find that SG stars show, on average, a Li abundance higher by 0.1 dex than MS
stars. We also detect a positive slope of Li abundance with effective
temperature, the higher the temperature the higher the Li abundance, both for
SG and MS stars, although the slope is slightly steeper for MS stars. These
results provide an unambigous evidence that the Li abundance changes with
evolutionary status. The physical mechanisms that contribute to this are not
yet clear, since none of the proposed models seem to describe accurately the
observations. Whether such mechanism can explain the cosmological lithium
problem, is still an open question.
