Reference for Ketubot 197:4

מהו דתימא התם הוא דאיסתלקא לה מהאי ביתא לגמרי אבל הכא ניגזור מנה ראשון אטו מנה אחרון קא משמע לן

What might I have said? There because [by her one act] she completely severed her connection with that house, but here [the sale for] the first maneh should be disqualified because the sale of the last maneh is invalid, therefore it teaches us that it is not.

Jastrow