Shevuah on Mitzvos

Question

You can’t make a Shevuah against the mitzvos (ie: I won’t shake a Lulav). But can you make a double Shevuah, that neither goes against a mitzva, but together does(ie: I won’t shake any Lulav in this town. Then, I won’t leave this town)?

Answer 1

It would take effect, because neither oath directly contravenes a mitzvah. See Mishneh Torah, Shvuot 5:18:

נִשְׁבַּע שֶׁלֹּא יֹאכַל מַצָּה שָׁנָה אוֹ שְׁנָתַיִם. הֲרֵי זֶה אָסוּר לֶאֱכל מַצָּה בְּלֵילֵי הַפֶּסַח וְאִם אָכַל חַיָּב מִשּׁוּם שְׁבוּעַת בִּטּוּי. וְאֵין זֶה שְׁבוּעַת שָׁוְא שֶׁהֲרֵי לֹא נִשְׁבַּע שֶׁלֹּא יֹאכַל מַצָּה בְּלֵילֵי הַפֶּסַח אֶלָּא כָּלַל עִתִּים שֶׁאֲכִילַת מַצָּה בָּהֶם רְשׁוּת עִם עֵת שֶׁאֲכִילָתָהּ בּוֹ מִצְוָה וּמִתּוֹךְ שֶׁחָלָה שְׁבוּעָה עַל שְׁאָר הַיָּמִים חָלָה עַל לֵיל הַפֶּסַח. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה. כְּגוֹן שֶׁנִּשְׁבַּע שֶׁלֹּא יֵשֵׁב בְּצֵל סֻכָּה לְעוֹלָם אוֹ שֶׁלֹּא יַעֲלֶה עָלָיו בֶּגֶד שָׁנָה אוֹ שְׁנָתַיִם

One who takes an oath not to eat matzah for a year or two is forbidden to eat matzah on the nights of Pesach. If he eats it, he is liable, for violating a sh'vuat bitui. This is not considered as an oath taken in vain, since he did not take an oath [specifically] not to eat matzah on the nights of Pesach. Instead, he included the times when eating matzah is a matter of choice together with those when it is a mitzvah. Since the oath takes effect with regard to the other days, it also takes effect with regard to Pesach. Similar laws apply in all analogous situations, e.g., one took an oath not to sit in the shade of a sukkah forever, or not to wear a garment for a year or two.

See also Shulchan Aruch, Yoreh Deah 236:5.