"Business-method-software" patents have been strongly debated. PTO's examiners are accused of granting patents to non deserving-innovations. But innovators are liable too, as they do not search for the relevant prior art. We propose a model of bilateral search of information. The innovator undertakes a costly search of prior art, and becomes privately informed of the value of the innovation. Then, he applies for a patent and reveals some prior art to the PTO. The PTO performs a complementary search to assess the patentability of the innovation. An innovator can conceal some information to increase the probability of being granted a patent. To induce the innovator to search for more prior art, the PTO should commit to an assessment contingent on the quantity of prior art revealed by the innovator.