Before revision:  Boundary faces in a B-rep model could be connected in a smooth manner, typically G1 continuous, for functional, manufacturing or aesthetic reasons. Quite often, it is desirable to preserve such smooth connections during push-pull moves .
After revision:  Boundary faces in a B-rep models being used are quadric models (composed of linear and quadric surfaces). However, push-pulling such models is not trivial due to the possible smooth face-face connections in the models. The major issue is that, during push-pull moves .