In the framework of ARISE project (Automatic Railways Inquiry Systems for Europe) we developed DEMON, a real time spontaneous speech dialogue system allowing mixed initiative. This system gives information for train connection. On this system three different confirmation strategies were developed and compared with regard to erroneous confirmation rates. The first strategy was implicit confirmation question oriented. Those questions were used as widely as possible. Refutation for those questions appeared to be quite low. The reordering of parameters in implicit questions to match the order of mental