System for locking and unlocking an opening, wherein the system comprises: - a movable bolt which is designed to deploy and retract during closing and opening of the opening, wherein the bolt is designed to occupy a first deployed position when the opening is closed and a second deployed position when the opening is open, - a movable locking part which is designed to interact with the bolt, wherein the locking part is designed, firstly, to occupy a locking position in which it prevents the passage of the bolt from its first deployed position to its retracted position in the absence of external action on the part, and, secondly, the passage from its locking position to an unlocking position under the action of an external force to allow the opening of the opening, wherein the system comprises a movable counter-bolt which is designed to deploy and retract during the closing and opening of the opening, and wherein the counter-bolt is designed to prevent the return of the locking piece from its unlocking position to its locking position when the bolt is in its second deployed position and the opening is open, wherein the bolt and the counter-bolt are each mounted on the same first axis of rotation and are able to pivot about the axis of rotation independently of one another over a given angular range of rotation, wherein the bolt comprises a front face that is intended to interact with a striker and a so-called locking rear face that is designed to interact with the locking part, wherein the front face of the bolt has a convexity which is centered on a centering axis of the front face, wherein the centering axis of the front face and the first axis of rotation are offset in order to create a torque allowing the closing of the opening when the front face of the bolt comes into contact with the striker and/or the frame on which the striker is mounted. - a movable bolt which is designed to deploy and retract during closing and opening of the opening, wherein the bolt is designed to occupy a first deployed position when the opening is closed and a second deployed position when the opening is open, - a movable locking part which is designed to interact with the bolt, wherein the locking part is designed, firstly, to occupy a locking position in which it prevents the passage of the bolt from its first deployed position to its retracted position in the absence of external action on the part, and, secondly, the passage from its locking position to an unlocking position under the action of an external force to allow the opening of the opening, wherein the system comprises a movable counter-bolt which is designed to deploy and retract during the closing and opening of the opening, and wherein the counter-bolt is designed to prevent the return of the locking piece from its unlocking position to its locking position when the bolt is in its second deployed position and the opening is open, wherein the bolt and the counter-bolt are each mounted on the same first axis of rotation and are able to pivot about the axis of rotation independently of one another over a given angular range of rotation, wherein the bolt comprises a front face that is intended to interact with a striker and a so-called locking rear face that is designed to interact with the locking part, wherein the front face of the bolt has a convexity which is centered on a centering axis of the front face, wherein the centering axis of the front face and the first axis of rotation are offset in order to create a torque allowing the closing of the opening when the front face of the bolt comes into contact with the striker and/or the frame on which the striker is mounted.