in the straight direction of the arm 32 when the gear 46 meshes with the circular toothed portion 72 the rotation of the crank 40 controls a swinging of the arm 32 about a fixed axis with reference to fig3 and 6 9 the opening closing device 16 comprises a first slider 80 and a second slider 82 intended to be slidably mounted within a longitudinal groove of the lower horizontal side of the wing 14 the first slider 80 is articulated to the distal end of the arm 32 by a pin 84 the second slider 82 is connected to a connecting rod 24 which is in turn connected to the lower corner drive 26 of the locking device 18 the second slider 82 carries a closing element 88 which is intended to cooperate with a respective striker 20 fixed to the frame 12 preferably the closing element 88 is integrally formed with the second slider 82 the closing element 88 is preferably provided with a pin 90 which engages a corresponding hole of a connecting rod 24 the first slider 80 and the second slider 82 are connected together in a releasable manner by means of a hook 90 articulated to the slider 80 the hook 90 has a seat 92 which engages u2014 in a releasable manner u2014 a pin.