A vast majority of the time, petitioners in USPTO post-grant proceedings attempt to show invalidity of challenged claims by showing the prior art explicitly discloses all limitations of the claims. A petitioner in a recent Inter Partes Review (IPR) proceeding successfully invalidated claims of U.S. Patent No. 5,930,444 (the “‘444 patent”), titled “Simultaneous Recording and Playback Apparatus,” by establishing some of the claim limitations are inherently present in the prior art.