The main theme of volume 4 is prophylaxis, a concept first expounded by Nimzowitsch and one which has been brilliantly developed by Mark Dvoretsky and his pupils. The art of positional play is explained in terms of planning, manoeuvring, the study of typical positions, and deep strategy in grandmaster games. The main theme of volume 4 is prophylaxis , a concept first expounded by Nimzowitsch and one which has been brilliantly developed by Mark Dvoretsky and his pupils. The art of positional play is explained in terms of planning, manoeuvring, the study of typical positions, and deep strategy in grandmaster games.