  We present a stability analysis of the two-dimensional t-t' Hubbard model for
various values of the next-nearest-neighbor hopping t', and electron
concentrations close to the Van Hove filling by means of the flow equation
method. For t' > -t/3 a d_{x^2-y^2}-wave Pomeranchuk instability dominates
(apart from antiferromagnetism at small t'). At t' < -t/3 the leading
instabilities are a g-wave Pomeranchuk instability and p-wave particle-hole
instability in the triplet channel at temperatures T < 0.15t, and an
s^*-magnetic phase for T > 0.15t; upon increasing the electron concentration
the triplet analog of the flux phase occurs at low temperatures. Other weaker
instabilities are found also.
