Renvers is in fact the mirror-exercise of the haunches-in and has the exact same gymnastic effect. The difference: the wall is on the other side.
Haunches in: Renvers:
Renvers is a side movement on three or four tracks in which the horse looks where it is going. In this exercise, the horse is also bended laterally from neck to tail. The outside hind leg is stepping under the weight. The hindquarter walks on the track along the wall, the shoulders on the inside track. This is in contrast to the hindquarter-in where the shoulders follow the wall and the hindquarter walks on the inside track.