This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
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Testing Expressions
Mathematica symbolic expressions can represent an immense range of types of objects. Mathematica provides a rich collection of functions to test expressions. Functions that "ask a question" have names that end in Q. They return True for an explicit true answer, and False otherwise.
Equality & Inequality
Equal (==), Unequal (!=) — numerical equality
SameQ (===), UnsameQ (=!=) — literal symbolic identity
Less(< ▪ Greater(> ▪ LessEqual(<= ▪ GreaterEqual(>=)
And(&& ▪ Or(|| ▪ Not(! ▪ True  ▪ False  ▪ ...
NumberQ, MachineNumberQ literal number, literal machine-precision number
NumericQ numeric quantity (consisting of numbers, numeric constants, and functions)
IntegerQ  ▪ EvenQ  ▪ OddQ  ▪ PrimeQ  ▪ CoprimeQ  ▪ AlgebraicIntegerQ  ▪ ...
List-Oriented Tests
VectorQ, MatrixQ vector, matrix, perhaps with elements of specified types
ArrayQ full array of any depth
MemberQ test whether a pattern occurs in a list
Expression Tests
MatchQ test whether an expression matches a pattern
AtomQ  ▪ TrueQ  ▪ OrderedQ  ▪ PolynomialQ
StringQ  ▪ StringMatchQ  ▪ StringFreeQ  ▪ LetterQ  ▪ DigitQ  ▪ SyntaxQ  ▪ ...