Nedarim 6b - Yados by Kiddushin

The gemara has a question whether there are yados by kiddushin, peiah, tzedaka, hefker and hasmana l'beis hakisei. Although "yad" is a gezerias hakasuv in the context of neder (and applies to nezirus based on a hekesh or visa versa), it would certainly apply to korbanos since that is also a form of neder. The gemara explains the tzad that it would apply to peiah, tzedaka, and even hefker is also based on the hekesh. However, it is unclear what the source would be that yad should work by kiddushin. The Ran explains that it would be based on a 'ma matzinu' from nedarim.

Based on the Ran before 4b that a 'ma matzinu' cannot give you malkus (the mishne l'melech is not sure; see maharatz chiyus that it depends on why there is no malkus from kal v'chomer - if it is bec. a kal v'chomer is not strong enough to give malkus then certainly a ma matzinu is not strong enough, but if it is because malkus may not be strict enough for the chamur and is only a kapara for the kal, then by a ma matzinu where the two are equal there is malkus -v'dok), if yados kiddushin are learned from a ma matzinu, there should be no misah for a woman who is mikudeshes through yados and commits adultery since 'ein onshin min hadin' (l'maseh that we leave with a safek whether there are yados by kiddushin, just that we are machmir, there would anyway be no punishment for adultery because we can't punish her m'safek). However, according to the Rosh who understands that tzad that there is yad by kiddushin is based on the language being similar to hekdesh, not a 'ma matzinu', then on the tzad that there are yados by kiddushin she would be punished for adultery.

Another advantage to the Rosh, is that R' Akiva Eiger asks that according to the Ran that the hold tzad not to learn kiddushin from a ma matzinu from nedarim is that it involves a ma'aseh and not just dibur, then it should be obvious that we learn tzedaka from a ma matzinu from nedarim (even without a hekesh), so why does the gemara have a question (see poras yosef who answers that when one says selah zu l'tzedaka, can still change his mind until given to the gabai, so we see that action also plays a role similar to kiddushin). According to the Rosh the whole question doesn't start since he never entertains that a ma matzinu is a valid source to learn yados from (since we can easily come up with a pircha as we see in the gemara on 4b), so 'ma matzinu' is not a possible source for yados by tzedaka and the only possible source is the hekesh.