Comedian Ari Shaffir performs at the 2015 Bonnaroo Music and Arts Festival in June in Manchester, Tenn. Shaffir has said fellow comedian Carlos Mencia stole his joke about who would build a fence on the U.S.-Mexican border. Copyright on jokes is difficult to prove, and it turned out two other comedians had made similar jokes as well. John Davisson/Invision/AP hide caption

itoggle caption John Davisson/Invision/AP

This week, a judge in Pennsylvania moved forward with a lawsuit against the members of Led Zeppelin and their music publishers. The band is accused of plagiarism. Dario Cantatore/AP hide caption

itoggle caption Dario Cantatore/AP

Jimmy Page, Robert Plant, and John Bonham of Led Zeppelin, in 1970. A new lawsuit says the group borrowed from another band's work without crediting it, for the huge hit "Stairway to Heaven." Roger Jackson/Getty Images hide caption

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Sen. Rand Paul, R-Ky., is sorry for the plagiarized material in his speeches and op-eds. And he thinks some journalists are just plain sorry. Jose Luis Magana/AP hide caption

itoggle caption Jose Luis Magana/AP