Date: 5561
From: Rabbi Moshe Sofer
To: Mattersdorf
The Chasam Sofer composed a comprehensive conditional marriage document (nusach shtar kiddushin al tenai) for use in Mattersdorf, making all stages of marriage — kiddushin, chuppah, yichud, and bi'ah — contingent on specified conditions. If the husband dies childless without giving a get and his brother fails to perform chalitzah within one year, the entire marriage is retroactively void, freeing the woman without need of yibum or chalitzah. The document includes a solemn oath al daas rabbim to prevent annulment of the conditions.
Source: Shu"t Chasam Sofer EH I §111