From: Rabbi Mordechai Leib Winkler
To: Rabbi Aharon Ged Katz
The responsum discusses the permissibility of tying a knot on a tie over an existing knot on Shabbat, specifically in the context of a Torah scroll cover, and the definition of a 'kesher shel kayama' according to the Mordechai and Taz.
Source: Orach Chayim II §81