We say that the proof that a Get is no better than Maamar and Maamar is no better than Get is from the Shita of R' Gamliel. Although he holds that once a Get is given to one Yevama then a second Get to a different one does not take effect (and doesn't disqualify her to marry the brother's relatives.) The same thing applies with giving Maamar after a Maamar. However, he allows a Maamar to take effect after a Get and a Get after a Maamar. So we must say they're even.
Tosfos asks: This last Halacha is true even to the Rabanan (that hold that there is Get after Get and Maamar after Maamar), so why does the Gemara only bring a proof from R' Gamlilel?
Tosfos answers the Rabanan that hold a second Get take effect after the first Get despite that it must be weaker (since the first Get was the one that "divorced" her and the second is "divorcing" someone who is already "divorced".) Therefore, even if Maamar or Get is stronger than the other, it will still take effect.
However, R' Gamliel who holds the second Get or Maamar doesn't take effect after the first, because he holds that a weaker transaction can't take effect on a stronger transaction. Therefore, since a Get takes effect on a Maamar and a Maamar takes effect on Get, we must conclude that one is not weaker than the other and therefore they're even.
Rabbi Chaim Smulowitz
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