If[condition, t, f] gives t if condition evaluates to True, and f if it evaluates to False. If[condition, t, f, u] gives u if condition evaluates to neither True nor False.

Mathematica provides various ways to set up conditionals, which specify that particular expressions should be evaluated only if certain conditions hold. Conditional ...

Relational operators. This tests whether 10 is less than 7. The result is False. Not all of these numbers are unequal, so this gives False.

While most built-in Mathematica functions follow the standard evaluation procedure, some important ones do not. For example, most of the Mathematica functions associated with ...

NonPositive[x] gives True if x is a non-positive number.

NonNegative[x] gives True if x is a non-negative number.

StringQ[expr] gives True if expr is a string, and False otherwise.

ValueQ[expr] gives True if a value has been defined for expr, and gives False otherwise.

DigitQ[string] yields True if all the characters in the string are digits in the range 0 through 9, and yields False otherwise.

VectorQ[expr] gives True if expr is a list or a one-dimensional SparseArray object, none of whose elements are themselves lists, and gives False otherwise. VectorQ[expr, ...