  A complete basis for the next-to-next-to leading order heavy-to-light
currents in the soft-collinear effective theory is constructed.
Reparameterization invariance is imposed by deriving constraint equations.
Their solutions give the set of allowed Dirac structures as well as relations
between the Wilson coefficients of operators that appear at different orders in
the power expansion. The completeness of reparameterization invariance
constraints derived on a projected surface is investigated. We also discuss the
universality of the ultrasoft Wilson line with boundary conditions.
