what is proposed is an inwardly articulated form assembly for forming concrete core - wall structures having a rectangular shape in which a primary form structure having fixed seamless corners is presented to the wet concrete ; after the concrete has set , a secondary support structure which effects a compound movement when activated by a lever assembly connected thereto causes the primary form to articulate inwardly in a progressively centripetal movement towards the interior of the core - shaft about vertically extending double hinged seams in the wall faces of the primary form near respective corners thereof .