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NumberQ
NumberQ[
expr
] gives True if expr is a number, and False otherwise.
NumberQ[
expr
] returns False unless expr is manifestly a number (i.e., has head Complex, Integer, Rational or Real).
NumberQ[Infinity] gives False.
NumberQ[Overflow[
]] and NumberQ[Underflow[
]] give True.
You can use NumberQ[
x
]
=
True to override the normal operation of NumberQ, and effectively define x to be a number.
See the Mathematica book: Section 2.3.5, Section 3.1.1.
See also: NumericQ, IntegerQ, TrueQ.
Further Examples
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