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Claim 1

A UNITARY CLOSURE FOR SEALING AN OPENING IN A CONTAINER IN WHICH THE CONTAINER IS PROVIDED WITH A SUBSTANTIALLY FLAT ANNULAR SEAT ABOUT THE OPENING HAVING MEANS ADJACENT THE OPENING CAPABLE OF ENGAGING CORRESPONDING MEANS ON THE CLOSURE FOR HOLDING THE CLOSURE IN POSITION THEREON, COMPRISING: (A) A CYLINDRICAL SIDE PORTION HAVING MEANS CARRIED THEREON FOR ENGAGING THE HOLDING MEANS CARRIED ON THE CONTAINER FOR HOLDING THE CLOSURE IN SEALED ENGAGEMENT WITH THE SEAT; (B) A CONTINUOUS TOP PORTION FORMED INTEGRAL WITH THE SIDE PORTION AND POSITIONED IN A PLANE ABOVE THE HOLDING MEANS CARRIED BY THE SIDE PORTION OF THE CLOSURE; (C) THE TOP HAVING A SUBSTANTIALLY RIGID CENTER PORTION, A SUBSTANTIALLY RIGID CONTINUOUS ANNULAR SEAT ENGAGING PORTION INCLUDING AN INNER SEAT CONTACTING SURFACE EXTENDING ABOUT THE CENTRAL TOP PORTION ENGAGING THE ANNULAR SEAT ABOUT THE CONTAINER OPENING, AND CONNECTED TO THE RIGID CENTER PORTION BY AN ELASTIC FLEXBLE PORTION, THE INNER SURFACE OF THE ANNULAR SEAT ENGAGING PORTION BEING ANGLED DOWNWARDLY FROM A HORIZONTAL PLANE PASSING THROUGH THE LOWER OUTER EDGE THEREOF, THE SAID INNER SURFACE OF THE SEAT ENGAGING PORTION BEING PROVIDED WITH A PLURALITY OF RAISED CIRCULAR RINGS OF DIFFERENT HEIGHTS OF RINGS PROGRESSIVELY INCREASING IN HEIGHT IN THE DIRECTION OF THE CENTER OF THE CLOSURE; (D) A CONTINUOUS RESILIENT FLEXIBLE HINGE PORTION OF LESS RIGIDITY THAN THE ANNULAR SEAT ENGAGING PORTION EXTENDING UPWARDLY AND OUTWARDLY AT AN ANGLE FROM THE OUTER EDGE OF THE RIGID SEAT ENGAGING PORTION AND OUT OF POSITION TO CONTACT THE ANNULAR SEAT ABOUT THE CONTAINER OPENING, THE FLEXIBILITY OF THE HINGE PORTION BEING OF SUCH RESISTANCE AS TO PREVENT LEAKAGE BETWEEN THE CONTAINER SEAT AND THE SEAT ENGAGING PORTION OF THE CLOSURE, THE UPPER OUTER EDGE OF THE FLEXIBLE HINGE PORTION BEING CONNECTED TO THE CYLINDRICAL PORTION ALONG A LINE WHICH IS IN A PLANE ABOVE THE PLANE OF THE SEAT ENGAGING PORTION, THE FLEXIBLE HINGE BEING MOVED UPWARDLY FORMS A RESILIENT STRESS AREA BETWEEN THE SEAT ENGAGING PORTION AND THE CYLINDRICAL PORTION WHEN THE TOP PORTION IS MOVED UPWARDLY RELATIVE TO THE CYLINDRICAL PORTION; WHEREBY THE SEAT ENGAGING PORTION IS URGED DOWNWARDLY AND IN SEALED ENGAGEMENT WITH THE SEAT ABOUT THE CONTAINER OPENING WHEN THE SEAT ENGAGING AREA IS MOVED UPWARDLY BY THE CONTAINER SEAT TO PLACE THE FLEXIBLE HINGE UNDER STRESS.