[ Resolution proposed by ballot comment: ]

unlock should specifiy the precondition that the current thread "owns the lock", this will make calls without holding the locks "undefined behavior". unlock in [mutex.requirements] should either be noexcept(true) or be allowed to throw system_error like unique_lock::unlock, or the latter should be nothrow(true) and have the precondition owns == true. Furthermore unique_lock's postcondition is wrong in the case of a recursive mutex where owns might stay true, when it is not the last unlock needed to be called.

Addresses CH-26

Specifications of unlock member functions and unlock mutex requirements are inconsistent wrt to exceptions and pre- and postconditions.