Yevamos Chapter 10, Mishnah 5. This Mishnah is essentially similar to the previous one, except that in the previous Mishnah the woman married the same man twice, while here we are dealing with a series of marriages to different men - some of which ended in mi'un (refusal) and some in a get.
The sequence of marriages in the Mishnah:
"HaMema'enes ba'ish" - a minor who annulled her first marriage by declaring mi'un against her husband.
"V'nises l'acher v'girshah" - she married a second husband, and that marriage ended with a get that he gave her.
"L'acher u'mi'anah bo" - she married a third husband, and while still a minor she declared mi'un against him and annulled the marriage.
"L'acher v'girshah" - she married a fourth husband, and he gave her a get.
"L'acher u'mi'anah bo" - she married a fifth husband, and this marriage ended in mi'un.
The ruling that emerges from the Mishnah:
"Kol sheyatz'ah heimenu b'get - asurah lachzor lo" - any husband from whom she left with a get is forbidden to her to return to, because she had an additional marriage with another man afterward.
"B'mi'un - muteres lachzor lo" - any husband from whom she left through mi'un she may return to, since we view that marriage as though it was never a valid marriage in the first place.
In summary: even when a woman has gone through many marriages to different men, the ruling is determined by the manner in which she left each one: leaving with a get forbids her to return to that husband because of the marriage that followed it, while leaving through mi'un leaves her permitted to return to him, because that marriage is nullified retroactively.