From: Rabbi Mordechai Leib Winkler
To: Rabbi Yisrael Avraham Alter Landau
The responsum discusses a case where a Brit Milah was on the first day of Pesach, and whether it was permissible for a non-Jew to transport the infant by train to the mohel's location on Yom Tov, considering it a rabbinic prohibition.
Source: Orach Chayim III §47