_________ agrees that so long as the building shall remain standing, _________ shall have the right to have the building now erected, overlap and extend beyond the north line of the land of _________, and to encroach and rest on the land of _________ to the same extent and in the same manner as the building now overlaps and encroaches on the land of _________. This agreement shall remain in force and effect only so long as the present wall of the building shall remain standing, and that on removal or destruction of the wall, all rights of _________ under this agreement, shall cease and determine.