premise: 4. Immediately upon a request by the Disclosing Party at any time, the Receiving Party will turn over to the Disclosing Party all Proprietary Information of the Disclosing Party and all documents or media containing any such Proprietary Information and any and all copies or extracts thereof or upon request of the Disclosing Party, the Receiving Party shall certify in writing that all materials containing Proprietary Information (including all copies thereof) have been destroyed. 