Hello kollel!
1)
Here's an offbeat q. I am a firstborn. I know we say eid echod neeman be issurim, but how do I trust my parents that I'm a bechor and also not born by C-section etc? Bc there's no issur there, and I have no proper witnesses.
Maybe there's a rav moshe angle that I'm a "bechor ha-companies" bc of my New York state birth certificate? :-)
2) I believe there are opinions the female firstborns are chayav, even though in practice we don't hold that way. To be lifnim mishuras hadin, is it appropriate for firstborn girls to go to the siyum in shul to be included according to those shitos?
My cousin answered the first question! Based on the fact there's a special verse and din of "yakir" that lets the father designate the bechor.
Thank you and a chag kasher vesameach!
1)
(a) Rabbi Yehuda stated in Kidushin 74a that a man is beleived to say "this is my firstborn son".
(b) Halichot Shlomo (Nissan-Av) chapter 8 note 2, page 180, cites Rav Shlomo Zalman Auerbach zt'l in the name of the Divrei Shaul (by Rav Yosef Tzvi Natanzon, the author of Shoel uMeishiv) that according to the Chok Yaakov Orach Chaim 470:2 (printed on the page of the Shulchan Aruch) a C-section bechor should also fast.
2) Halichot Shlomo there cites the Maharil that female firstborns shouild also fast, but the Rema in Shulchan Aruch Orach Chaim 470:1 writes that the custom does not follow the Maharil. However the Rabbanit of Rav Shlomo Zalman Auerbach was a firstborn, so her husband used to bring her something to taste from the Seuda of the Siyum.
Apologies that this reply did not arrive before Pesach.
Kayitz Bari!
Dovid Bloom