Summary

Yosef Karo Shulchan Aruch — Choshen Mishpat 13

If the two judges agree, there are those that say that they do not need to select a third judge. There are those that say that if the defendant says he will choose two and the plaintiff can also choose two and they will select a fifth, the defendant is permitted to so because the more judges they have the more likely is it that the truth will prevail.
Paragraph 2- They would write so-and-so chose so-and-so and so-and-so chose so-and-so. A party may retract so long as it has not been written down. Once is had been written they can no longer retract.
Source: Wikisource

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