Reference for Gittin 17:10

<big><strong>גמ׳</strong></big> מאי אינו יכול לומר אילימא חרש חרש בר אתויי גיטא הוא והתנן הכל כשרין להביא את הגט חוץ מחרש שוטה וקטן

IF ITS VALIDITY IS CHALLENGED, IT MUST BE ESTABLISHED THROUGH THE SIGNATURES. Challenged by how many? Shall I say by one person? Has not R. Johanan laid down that a challenge must come from two at least? Shall I say then two? In that case there are two on each side, and why should you give credence to one set rather than to the other? — The challenge meant is that of the husband.

Jastrow