From: Rabbi Moshe Sofer
To: Rabbi Avraham
The Chasam Sofer upholds the Rema's ruling that the heirs of the zera kayama inherit the rights under a shtar chatzi zachar, rejecting the grandfather's umdana argument that he intended only to benefit his daughter or her direct descendants. He distinguishes between umdana applying to foreseeable events and its inapplicability to a hodaah (admission of receipt), concluding the grandfather has no valid basis to annul the document, though he advises the heirs to settle during the grandfather's lifetime.
Source: Shu"t Chasam Sofer EH II §159