a closure system consists of lock and several keys in which the closing of the lock , determined by mechanically or magnetically controllable tumblers , is variable in such a manner that a closure code of the lock which corresponds initially to the coding of the first key can be varied by rearrangement of at least one tumbler element within the lock , in response to the coding of a successor key . this negates need for a tool or hand knob . displacement of the tumbler element be effected by means of the corresponding successor key in the manner that successor keys are divided into a first region associated exclusively with a closure code of the tumblers and a second supplementation region e which enters into action when the first region agrees with the closure code of the tumblers . this shifts the tumbler element into the position acted on by the supplementation region of the next successor key .