In this paper, we treat strategic information exchange among subjects in a conflict that involves incompleteness of information in terms of subjects' preference and their interdependence. Then, we give two theorems that indicate senselessness of deceit. One of the theorems implies that any attempt of a subject to change another subject's preference by deceit will end in failure. The other theorem implies that deceit of a subject causes changes of preference of the subject, thus strategic information exchange cannot be effective.
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