Detailed Instructions: Given a sentence and two mentions from the text (arguments), indicate a phrase (a verb or noun phrase) that describes the relationship between the provided arguments.
Q: Sentence: 'Julia Rich Hogan concluded in her book about William Riche that John and Peter were brothers although she could not find any proof .', Argument/Subject 1: 'william', Argument/Subject 2: 'john'
A:
be brother of