Even thought most of the literature does not directly document this negative relationship there are several attempts to prove that discounting both complementary goods at the same time could be a protable strategy. Theoretical justication for holding sale on only one of two complements is grounded in the monopoly paradigm: if a shop lowers a price for one of the goods the optimal price for the other rises as the demand for it increases thus having both goods on sale should not be optimal. It is not obvious why, in the rst place, the monopolist has to lower one of the prices from its optimal monopoly level.
