For if according to ר"ג, he maintains that she is believed -דאי רבן גמליאל הא אמר איהי מהימנא
Summary:
According to the מ"ד that הטוען (פרעתי) אחר מעשה בי"ד נאמן, it is understood (even in the הו"א) that ר"ג agrees that the בעל is נאמן (if there are no עדי הינומא), since he has a מיגו of פרעתי.
Summary:
רש"י is of the opinion that the הנ"מ is proving that ר"ג is מודה בברי וברי. However תוספות insists that the הנ"מ is proving that ר"ג is מודה in a case that is similar to בו"ש.
There, an ox is slaughtered before you - התם שור שחוט לפניך
Summary:
According to רש"י the difference between שור שחוט and אין שור שחוט is if there is a claim or not. According to תוספות the difference is whether the counter claim to the מיגו is (basically) substantiated (as by טענת בתולים) or whether it remains unsubstantiated (as by שדה זו).