  We apply a renormalization group approach to the determination of the phase
diagram of the t-t' Hubbard model at the Van Hove filling, as function of t'/t,
for small values of U/t. The model presents ferromagnetic, antiferromagnetic
and d-wave superconducting phases. Antiferromagnetism and d-wave
superconductivity arise from the same interactions, and compete in the same
region of parameter space.
