Petersen, as he claimed, had a very independent way of thinking. In order to preserve this independence he made a habit to read as little as possible of other people's mathematics, pushing it to extremes. The consequences for his lack of knowledge of the literature of the time were severe. He spent a significant part of his time rediscovering already known results, in other cases already existing results had to be removed from a submitted paper and in other more serious cases a paper did not get published at all.
