<a href="http:&#x2F;&#x2F;www.unclaw.com&#x2F;chin&#x2F;teaching&#x2F;antitrust&#x2F;herfindahl.htm" rel="nofollow">http:&#x2F;&#x2F;www.unclaw.com&#x2F;chin&#x2F;teaching&#x2F;antitrust&#x2F;herfindahl.htm</a><p>disclaimer: recovering attorney who studied this in law school long ago. no longer practicing.