@techreport{plt-tr2009-htdc-v4.2, author = {Kathryn E. Gray}, title = {How to Design Classes Languages}, number = {PLT-TR2009-htdc-v4.2}, type = {Reference Manual}, institution = {PLT Scheme Inc.}, month = {June}, year = {2009}, url = {http://download.plt-scheme.org/doc/4.2/pdf/htdc.pdf}, note = {\url{http://plt-scheme.org/techreports/}} }