  Massless flows between the coset model su(2)_{k+1} \otimes su(2)_k
/su(2)_{2k+1} and the minimal model M_{k+2} are studied from the viewpoint of
form factors. These flows include in particular the flow between the
Tricritical Ising model and the Ising model. Form factors of the trace operator
with an arbitrary number of particles are constructed, and numerical checks on
the central charge are performed with four particles contribution. Large
discrepancies with respect to the exact results are observed in most cases.
