  We study inclusive Lambda hyperon production in pp collisions at BNL RHIC,
with just one transversely polarized proton. We show that the measurement of
the spin transfer between the initial proton and the produced Lambda is
sensitive to the proton transversity distributions and to the corresponding
Lambda transversity fragmentation functions. In view of our present ignorance
of these distributions and fragmentation functions, we resort to positivity
bounds for making some predictions for the corresponding spin transfer
asymmetry.
