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based on an earlier version of the Wolfram Language.
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HoldFirst

HoldFirst
is an attribute which specifies that the first argument to a function is to be maintained in an unevaluated form.
Definitions for unevaluated expressions can implement call-by-name semantics:
The global variable has been modified:
Functions that operate on symbols often need the HoldFirst attribute:
Assignments do not evaluate their left-hand sides:
Use Evaluate to force evaluation of an argument of a HoldFirst function:
Suppress the evaluation of the first argument of a pure function:
Sequence splitting still happens for HoldFirst functions:
NHoldFirst protects arguments from N, but evaluates them normally otherwise:
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