Examples of known locks of the aforesaid kind are described and illustrated in CH-A-650 054 (Berchtold), US-A-4 068 510 (Nearyl), US-A-1 639 535 (Russo), US-A-1 116 929 (Schoell) and FR-A-2 177 148 (Vachette).
None of these known lock arrangements or mechanisms, however, are constructed to prevent, with simple means, the lock from being opened with a standard key or guest key from the outside when the lock has been secured from the inside with the aid of a knob mechanism, while at the same time enabling the lock to be released from the outside with a special or management key.