Top: azimuthally-averaged angular velocity | Ω | (by absolute value). The positive/negative values are plotted by solid/dashed lines. A sharp drop in | Ω | indicates the radial position where the rotation changes its direction from counter-clockwise to clockwise. Bottom: azimuthally-averaged gas surface density. The solid circles indicate the position of the outer disk edge. The arrow shows the direction in which the disk shrinks thanks to the infall of external counter-rotating material.