Why "How so?" in Y'vamos 5:2?

Question

The Mishna, Y'vamos 5:1–2:

רבן גמליאל אומר, אין גט אחר גט ולא מאמר אחר מאמר ולא בעילה אחר בעילה ולא חליצה אחר חליצה. וחכמים אומרים, יש גט אחר גט ויש מאמר אחר מאמר אבל לא אחר בעילה ולא אחר חליצה כלום. כיצד? עשה מאמר ביבמתו ונתן לה גט, צריכה הימנו חליצה. עשה מאמר וחליצה, צריכה הימנו גט. עשה מאמר ובעל, הרי זו כמצוותה.‏

I'll summarize rather than translate: The Mishna first cites a dispute between R. Gamliel and the other rabbis. R. Gamliel says that if a man died childless and one of his brothers issued a get (bill of divorce) to one of the deceased's widows, then any subsequent get issued by a brother of the deceased's to a wife of the deceased has no effect; and the same is true of maamar (a sort of betrothal). The other rabbis disagree, stating that the second get or maamar has some effect. [I won't go into details about what the effect is.] That's the cited dispute; but R. Gamliel and the other rabbis agree that there's no effective intercourse after intercourse, nor effective chalitza after chalitza. Then the Mishna asks "How so?" and proceeds to explain simpler cases, in which there is no attempt at a get after a get, nor maamar after maamar, because there are only one widow and only one brother involved in the proceedings.

So what's the "How so?" doing there?

Answer 1

The Rav and others say simply that "How so?" is not referring to the preceding passage but the simpler rules on which the preceding passage is based. (Rambam says similarly but more specifically that "How so?" refers to the line "and there is nothing [effective] after intercourse or chalitza".)