(Rosh Yeshiva of Kaminetz and Torah Vodaas, 1886-1958).  Autograph Letter Signed written on letterhead in Hebrew to Rabbi Moshe Rothenberg.

Rabbi Reuven Grozovsky, son of Rabbi Shimon the Dayan of Minsk and son-in-law of the celebrated Rabbi Baruch Ber Leibowitz, was a leading Lithuanian Talmudist. Managing to escape Europe upon the onset of WWII, he settled in the United States, where he re-established the Kamenetzer Yeshiva, and was also active in both the Vaad Hatzalah and Agudath Israel. An engineer of the fledgling Torah community in post-war America, he founded the elite Beis Midrash Elyon in Monsey, New York. Rabbi Moshe Rothenberg was a product of Rabbi Meir Shapira's Yeshivath Chachmei Lublin. Upon arrival in the United States he re-established the yeshiva in Detroit, and later headed the Gerrer Yeshiva in Boro Park, Brooklyn. He authored Bikurei Aviv on Seder Kodashim, which was issued when he was just 20 years of age (and published just one day before Poland was invaded by the Nazis). See https://mishpacha.com/a-siyum-at-chachmei-lublin-detroit/.