Further Examples: Unevaluated

Unevaluated stops Plus from evaluating its arguments so the result is Plus. Unevaluated is transparent to Head.

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Here the arguments are evaluated so the result is no longer Plus.

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The algebraic expression remains unevaluated so terms with head Integer, Rational, or Real are returned.

In[3]:=

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Here the algebraic expression evaluates to a complex number, so there are no terms left with the specified heads.

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See also the Further Examples for Function.