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[[Dan Heisman]] <ref>[[Dan Heisman]] ('''1990, 1999, 2010, 2015''').''[http://www.danheisman.com/elements-of-positional-evaluation.html Elements of Positional Evaluation]''. Russell Enterprises</ref> represents an attempt at mathematical abstraction applied to chess, introducing seven concepts as fundamental in analyzing a chess position: mobility, flexibility, vulnerability, [[Center Control|center control]], piece coordination, time and speed. Heisman applies two [https://en.wikipedia.org/wiki/Dichotomy dichotomies]: ''actual'' versus ''potential'' and ''local'' versus ''global'':