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A set of technologies, that use radio waves for identifying people or objects, is called radio frequency identification system or RFID. RFID performance depends on tag and reader devices which use radio waves to communicate to each other. In some applications of RFID systems, the proof of concurrent presence for a number of objects or persons together in a given time is crucial. Grouping proof protocols are designed to address these needs, in fact grouping proof shows that two or more tags are evaluated by a reader simultaneously. This proof must be verified by the corresponding verifier. In this article this type of protocols are introduced and analyzed. At the first, the idea of designing a grouping proof is presented and then related protocols and their security analysis are presented. Finally, a comparison between protocols is provided.