  We state a variant of Arthur's weighted fundamental lemma for the metaplectic
group of Weil, which will be an essential ingredient of the stable trace
formula. Over a local field of large enough residual characteristic, we give a
proof using the method of descent, which is conditional upon the weighted
nonstandard fundamental lemma on Lie algebras. In view of the works of
Chaudouard and Laumon, this condition is expected to hold.
