; and (C) does not include a piece of material that has had— (i) its size or external shape altered solely to facilitate transportation or storage; or (ii) solely its chemical composition altered. ; and (4) by adding at the end the following: (36) The term ghost gun — (A) means a firearm, including a frame or receiver, that lacks a unique serial number engraved or cast on the frame or receiver by a licensed manufacturer or importer in accordance with this chapter; and (B) does not include a firearm that has been rendered permanently inoperable. . (b) Prohibition