A swing closure element (1), comprising: —a fixed structure (10) rigidly constrainable to an opening (11) of a door or window or the like, —a first movable wing (20) constrained to said fixed structure (10) by a first hinge constraint (21) so as to be pivotable about a first rotation axis (Z1), according to a predetermined opening rotation direction (W1), —a second movable wing (30) constrained to said first wing by said second hinge constraint (31) so as to be pivotable with respect to the first wing (20) about a second rotation axis (Z2), the first and the second wing (20, 30) being movable between a first closed configuration wherein they are coplanarly arranged to close the opening (11) and a second open configuration, —an articulated, quadrilateral mechanism (50, 50′) connected to the fixed structure (10) and to the second wing (30) comprising at least one stiffening member (61, 61′, 62, 62′) pivotably constrained to said first wing (20) and to a movable member (53, 53′) of said mechanism (50, 50′) connected to the fixed structure (10) and to said second movable wing (30).