  We reconsider the option of extracting the transversity distribution by using
interference fragmentation functions into two leading hadrons inside the same
current jet. To this end, we perform a new study of two-hadron fragmentation
functions. We derive new positivity bounds on them. We expand the hadron pair
system in relative partial waves, so that we can naturally incorporate in a
unified formalism specific cases already studied in the literature, such as the
fragmentation functions arising from the interference between the s- and p-wave
production of two mesons, as well as the production of a spin-one hadron. In
particular, our analysis clearly distinguishes two different ways to access the
transversity distribution in two-hadron semi-inclusive leptoproduction.
