Hooper）; Kenneth Whyld（英语：Kenneth Whyld）. The Oxford Companion to Chess（英语：The Oxford Companion to Chess）. Oxford University. 1996. ISBN 0-19-280049-3. 

Whyld. The Oxford Companion to Chess. Oxford University. 1996. ISBN 0-19-280049-3.  Dunnington, Angus. Winning Unorthodox Openings. Everyman Chess. 2000

方回應的步法稱為「防禦」。為人熟知的開局走法有好幾十種，而其中又有好幾百種被賦予名稱的變著。《牛津國際象棋大辭典（英语：The Oxford Companion to Chess）》列出了1,327有名稱的開局與變著，從平和的局面型走法，到激烈的戰術型走法通通包括在內。

Kenneth Whyld. The Oxford Companion To Chess. Oxford University. 1996. ISBN 0-19-280049-3.  Aagaard, Jacob. Dutch Stonewall. Everyman Chess. 2001. ISBN 9781857442526

David; Whyld, Kenneth, The Oxford Companion to Chess 2nd, Oxford: Oxford University, 1996, ISBN 0-19-280049-3  Kaufman, Larry, The Chess Advantage in Black