"I've written a book on gangs, taught a course on gangs at Occidental"

Tom Hayden's quote suggests that he has a great deal of knowledge and experience when it comes to gangs. He has actually composed a book on gangs, which suggests that he has done substantial research study on the topic and has a deep understanding of the subject. Furthermore, he has taught a course on gangs at Occidental, which recommends that he is an expert in the field and is capable of imparting his knowledge to others. This quote shows that Tom Hayden is an extremely knowledgeable and skilled person when it comes to gangs and can providing important insight into the subject.