Ketuboth page 20 side Tosphot brings the Yerushalmi. It comes out of the Yerushalmi that even if the witnesses on a doc of a loan remember nothing they ca still testify on their signatures and this is like Rav Hai Gaon brought in the Shita Mekubetzet, but not like the Rambam. I think the way to explain this difference is that Rashi, Tosphot and Ramban hold a document on a loan has validity from the Torah, and this is I think the reason of Hai Gaon. Since the doc is valid even without anyone saying anything in court, so to add extra validity to it, it is enough for witnesses to testify as to the validity of their signatures. However To the Rambam, documents of loans have no validity from the Torah, but the sages gave them validity so that the door will not be shut in front of people that want to borrow money. Let me bring here the Yerushalmi. The Mishna says R Judah Hanasi said when a document of a loan comes to court, the witnesses on it need to testify on the validity of their signatures, and also bring someone else to testify on each signature. But the sages said it is enough if each witness testifies on the validity of his own signature. the Yerushalmi says if no one remembers the loan, there is no argument between r Judah and the sages. both agree they testify on their signatures and bring another witness as for the same purpose. If both witnesses recall the loan, there is no argument. Everyone agrees that they testify as to the loan, and that is enough. The argument is when they recall the loan only after being reminded of it by the document. To the Yerushalmi the doc can be valid even if no one recalls the loan at all, and that is the opinion of Hai Gaon. To the Rambam this case is totally not valid. He bases himself on our Gemara and the fact that the doc is anyway no valid from the Torah. Our Gemara brings the Mishna and says Rav Huna said they need to recall the loan. R. Yochanan said if they recall the loan by being reminded by their own personal document, that is enough. The Rambam decided the law like R Yochanan and our Gemara.------------------------------------------------------------------------------------------------------------- כתובות תוספות בדף כ' ע''ב brings the ירושלמי. It comes out of the ירושלמי that even if the witnesses on a שטר of a loan remember nothing they ca still testify on their signatures and this is like האי גאון brought in the שיטה מקובצת, but not like the רמב’’ם. I think the way to explain this difference is that רש''י תוספות ורמב''ן hold a שטר on a loan has validity from the תורה, and this is I think the reason of האי גאון. Since the שטר is valid even without anyone saying anything in court, so to add extra validity to it, it is enough for witnesses to testify as to the validity of their signatures. However To the רמב’’ם, שטרי of loans have no validity from the תורה, but the sages gave them validity so that the door will not be shut in front of people that want to borrow money. Let me bring here the ירושלמי. The משנה says ר' יהודה הנשי said when a שטר of a loan comes to court, the witnesses on it need to testify on the validity of their signatures, and also bring someone else to testify on each signature. But the sages said it is enough if each witness testifies on the validity of his own signature. The ירושלמי says if no one remembers the loan, there is no argument between r Judah and the sages. both agree they testify on their signatures and bring another witness as for the same purpose. If both witnesses recall the loan, there is no argument. Everyone agrees that they testify as to the loan, and that is enough. The argument is when they recall the loan only after being reminded of it by the שטר. To the ירושלמי the שטר can be valid even if no one recalls the loan at all, and that is the opinion of האי גאון. To the רמב’’ם this case is totally not valid. He bases himself on our גמרא and the fact that the שטר is anyway invalid from the תורה. Our גמרא brings the משנה and says רב הונא said they need to recall the loan. ר’ יוחנן said if they recall the loan by being reminded by their own personal שטר, that is enough. The רמב’’ם decided the law like ר’ יוחנן and our גמרא.