The Tosefta understands this case totally differently. According to the Toesefta, here's what happened.
Reuven and Shimon testified against Mr. Ploni.
Then Yissochor and Zevulun made them aydim zo'me'min. So Mr. Ploni should go free and Reuven and Shimon should be killed.
Then Levi and Shimon made Yissochor and Zevulun aydim zo'me'min. So Reuven and Shimon should go free and Yissochor and Zevulun should be killed.
This can go on, and on, and on, and on...
However, Rebbe Yehuda says only the 1st pair can be executed. How can all of the pairs possibly have been with Yissachor and Zevulun????
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