I once encountered a fascinating Halachic question while praying in an airport before boarding. A group of nine Ashkenazim approached me and said they needed a tenth man so they could make a Minyan for Minha, and I of course happily agreed. During the Hazara (repetition of the Amida), an announcement was made that it was time to board. Six of us knew we had time to finish Minha before we needed to get on line to board, but four of the men were worried, and left to board. The remaining six were unsure what to do, and I told them that the Hazzan may continue the repetition of the Amida, since there was a Minyan in attendance when it began. If a section of the service requiring a Minyan began when ten or more men were present, it may be completed even if the Minyan was lost, as long as at least six men remain. The problem, however, arose when the time came to recite the Kaddish Titkabal after the Hazara. Ashkenazic custom views the Kaddish Titkabal as integrally connected to the Hazara, and therefore, just as the Hazara may be completed after the Minyan was lost, the Kaddish Titkaba after the Hazara may likewise be recited. Sephardic custom, however, views Kaddish Titkabal as separate from the Hazara, and thus according to Sephardic practice, if the Minyan was lost during the Hazara, then the Kaddish Titkabal may not be recited after the Hazzan completes the Hazara. I was thus unsure what to do in this situation, as a Sepharadi praying with Ashkenazim after four of the ten men left. Their Halachic tradition mandated reciting the Kaddish Titkabal after the repetition of the Amida, but according to my Halachic tradition, this Kaddish should not be recited. I did not know whether I should answer to their recitation of Kaddish. I later sent a message to Rav Yisrael Bitan asking this question, and he promptly replied with a detailed, six-page Teshuba (responsum) on this subject. He noted Hacham Ovadia Yosef's ruling that when a person hears a Beracha which according to his tradition is unwarranted, and thus recited in vain, he may not answer "Amen." One example is a Sefaradi who hears an Ashkenazi recite the Beracha of "Al Misvat Tefillin" over the Tefillin Shel Rosh. Although this Ashkenazi obviously acts correctly by reciting this Beracha, which is required according to Ashkenazic custom, the Sefaradi should not answer "Amen," since according to Sephardic practice, this Beracha constitutes a Beracha Le'batala (blessing recited in vain). This would apply also in the case of a Sefaradi who hears an Ashkenazi recite a Beracha over Hallel on Rosh Hodesh – a Beracha required by Ashkenazi custom but not according to Sephardic custom. Since Sephardic tradition regards this blessing as a "Beracha Le'batala," the Sefaradi should not answer "Amen" to this blessing. Many other Poskim dispute Hacham Ovadia's ruling, and maintain that since the Ashkenazi recites this blessing legitimately, in accordance with Ashkenazic practice, there is no problem for a Sefaradi to answer "Amen." Rabbi Bitan considers the possibility that Hacham Ovadia might agree that in the case of Kaddish, a Sefaradi may respond even if the Kaddish should not be recited according to Sephardic custom. One might distinguish between answering to an unwarranted blessing, which constitutes a "Beracha Le'batala," and answering to Kaddish, which is not a blessing. Rav Bitan concludes, however, that Hacham Ovadia likely applied his ruling even to Kaddish, and thus, in his view, a Sefaradi should not answer "Amen" to Kaddish if the Kaddish is not valid according to Sephardic custom. He may, however, answer "Yeheh Shemeh Rabba" even according to Hacham Ovadia's position, as this is merely an expression of praise, and differs from the response of "Amen." Given the different views on this subject, Rav Bitan suggested avoiding this problem by reciting the verse, "Baruch Hashem Le'olam Amen Ve'amen" (Tehillim 89:53 ), attempting to conclude the verse just when the others respond "Amen" to the Kaddish. This way, the Sefaradi answers "Amen" but says this word as part of a verse, which is always acceptable, thus satisfying all opinions.