“…On the other hand, many different procedures for verifying rule based expert systems are proposed, covering a broad range of methods [8,10,23,24,[27][28][29]41]. Unfortunately, the underlying semantics of the rules is not uniform: some systems interpret rules purely declarative as logical implications [25,28], whereas in other systems rules have an operational semantics, in which facts are added or removed from a pool of working knowledge (state space model) [8,14,27].…”