Muni's PlayIn The Grasshopper: Games, Life and Utopia (1978):
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To play a game is to attempt to achieve a specific state of affairs [prelusory goal], using only means permitted by rules [lusory means], where the rules prohibit use of more efficient in favour of less efficient means [constitutive rules], and where the rules are accepted just because they make possible such activity [lusory attitude].
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Playing a game is the voluntary attempt to overcome unnecessary obstacles.
Source: Bernard Suits, The Grasshopper