  We give a rigorous nonperturbative construction of a massless discrete
trajectory for Wilson's exact renormalization group. The model is a three
dimensional Euclidean field theory with a modified free propagator. The
trajectory realizes the mean field to critical crossover from the ultraviolet
Gaussian fixed point to an analog recently constructed by Brydges, Mitter and
Scoppola of the Wilson-Fisher nontrivial fixed point.
