Evolution with time of the pericenter longitude ϖ in three different models as in Fig. 1. In this case the planets have five and three Earth masses, respectively, and the inner one has a semimajor axis of 1 au. The disk potential causes a negative precession which adds up to that due to the mutual gravitational perturbations of the planets. As a consequence, the circulation rate of ϖ is negative in the full model with two planets and the disk potential (red line), contrary to what happens for massive planets within a disk gap. It is also faster compared to that observed in a pure three-body problem (blue line) and for a single planet (black line).