Christopher S. Velden; Timothy L. Olander; Raymond M. Zehr. Objective Dvorak Technique. University of Wisconsin–Madison. [2014-02-23]. (原始内容存档于2014-02-23).
Christopher S. Velden; Timothy L. Olander; Raymond M. Zehr. Objective Dvorak Technique. University of Wisconsin–Madison. [2014-02-23]. (原始内容存档于2014-02-23).