Top panel: evolution of the gas surface density, which is normalized against the initial gas surface density, across the protoplanetary disc for the nominal model with planets (solid lines) and without planets (dotted lines). The vertical dashed linesmark the semimajor axes of the planets, and they coincide with the locations of the three major gaps in the disc around HL Tau (Kanagawa et al. 2016). Bottom panel: evolution of the solid-to-gas surface density ratio across the protoplanetary disc for the nominal model. The solid component is divided into planetesimals (marked with gray) and dust+pebbles. Planetesimals form in narrow rings at the location of the gap edges and inside the planetary gaps (the amount of planetesimals formed inside the gaps is negligible). The interplanetary regions are depleted of dust and pebbles within a few hundred thousand years.