acting before the merger. Since the stellar particles in both disks are moving upwards in this plot in the parts of the disks that are already in touch, the tidal force distorted the disk so that the upper parts are closer than the lower ones. This results in the tumbling (clockwise around the $X$ axis) of the elongated shape after the merger seen in the lower right panel (view along the $X$ axis).

Simulation I90VY2 has the major axis inclined by 67deg with respect to the $X$ axis and lies in the $XY$ plane also being stable for the last 5Gyr of evolution. The position angles of the other axes vary by only about 30deg over the last 3 Gyr so this merger remnant does not show any significant figure rotation.

Orbit classification
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In this subsection, we focus on simulations which exhibit significant prolate rotation, so we exclude I90VY2 from further analysis.

At the beginning of the simulations stellar particles are situated in inclined disks on nearly circular orbits. During the merger particle orbits are transformed to form an object with a shape that can be well approximated by a triaxial ellipsoid. In static triaxial potentials most particle orbits 