From: Rabbi Akiva Eiger
To: Unknown recipient
Rabbi Shlomo Eiger distinguishes between a simple claim of 'I am divorced' and the Kesubos 22a case with conflicting witnesses: in the latter, the woman's permission to remain married rests on her bari li certainty claim, which restores the deterrent of mitoch chumrah and makes ein ishah me'izah operative. Rabbi Akiva Eiger endorses this analysis as supporting the Rema's interpretation of the Rosh against the Beis Yosef, but later expresses doubt about the reliance on einehah nasnah b'acher.
Source: Shu"t Rabbi Akiva Eiger §173