RuleDelayed

or
represents a rule that transforms lhs to rhs, evaluating rhs only after the rule is used.

DetailsDetails

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Basic Examples  (1)Basic Examples  (1)

holds its right-hand side unevaluated:

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The right-hand side is evaluated separately each time it is used:

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Introduced in 1988
(1.0)
| Updated in 1996
(3.0)