Responsa for Bava Batra 45:9

צריכא דאי אשמעינן התם גבי רשות הרבים דאימור כונס לתוך שלו הוא אי נמי אחולי אחול בני רשות הרבים גביה אבל הכא לא

R. JUDAH SAYS THE SPACE SHOULD BE SUFFICIENT FOR THE SOWING OF FOUR… HE HAS A RIGHT etc. R. papa [or, according to others, R. Zebid] said: This implies that the <i>Beth Din</i> may plead the cause<span class="x" onmousemove="('comment',' I.e., if a man inherits a property from his father and another man claims it, if it is proved that the father occupied it for three years, the Beth-Din can plead on behalf of the heir that the father had originally bought it from the man, whereas they would not do so for the father, if he did not put forward the plea on his own account. Similarly with a man who has bought a field which is then claimed by a third party. ');">¹³</span> of an heir and may plead the cause of a purchaser. But we have already learnt the rule about the heir in the following statement: 'He who claims [a property] qua heir has no need to plead [that his father bought the property]'?<span class="x" onmousemove="('comment',' Because, if the father has occupied it three years. the Beth-Din assume this without his pleading it. V. infra 410. ');">¹⁴</span>

Teshuvot Maharam