<div dir="ltr"><div>RSF writes:</div>
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<div>>> I have a question about when 9 Av falls out on Sunday, as it did this year. </div>
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<div>The halacha is that the fast starts at shkiah. Why is it that we're allowed to fast on Shabbos for 9 Av, especially when Shabbos is docheh 9 Av? Since Bein Hashmashot is a safeik, why don't we see safeik d'oraita l'chumrah in the case of oneg Shabbos, and safeik d'rabbanan l'hakeil in the case of Tisha B'av? <<</div>
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<div>1) Oneg Shabbos is not D'Oraysa, but MiDivrei Neviim.</div>
<div>2) Missing a few minutes of ability to eat is not a Bittul Oneg Shabbos and it isn't fasting - you've eaten all day.</div></div>