This is documentation for Mathematica 6, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.1)
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 (SameQ), UnsameQ (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  ▪ ...