Bava Batra 63 - No Unnecessary Terms in Legal Documents
If an ineffectual clause appears in a legal document, it is reinterpreted in such a way that it is effectual.
For example, if one sells a house to his fellow and says to him, "I am selling you this house with the stipulation that the fenced rooftop is mine" - the fenced rooftop is his. The clause "rooftop is mine" is redundant. It is already his, as we have learned before . Therefore, this clause is reinterpreted to give him additional rights.
Exactly which rights he gets is subject to a dispute: either that he may project beams from the roof into the adjacent yard, or that he may rebuild it if it collapses, with the second view prevailing.