Howard Staunton (1873). “The Chess-player's Handbook: A Popular and Scientific Introduction to the Game of Chess, Exemplified in Games Actually Played by the Greatest Masters, and Illustrated by Numerous Diagrams of Original and Remarkable Positions”, p.34
"The Most Instructive Games of Chess Ever Played : 62 Masterpieces of Chess Strategy". Book by Irving Chernev, Game 18 : The Isolated Pawn (p. 81), 1965.
Howard Staunton (1873). “The Chess-player's Handbook: A Popular and Scientific Introduction to the Game of Chess, Exemplified in Games Actually Played by the Greatest Masters, and Illustrated by Numerous Diagrams of Original and Remarkable Positions”, p.34