Before revision:  Quite often, it is desirable to preserve such smooth connections during push-pull moves . This is, however, no trivial matter and introduces additional challenges. To preserve the G1 connections , neighboring faces of push-pulled faces need to be made movable, but their motions are not known explicitly.
After revision:  Quite often, it is desirable to preserve such smooth connections during push-pull moves , neighboring faces of push-pulled faces need to be made movable, but their motions are not known explicitly.