Unevaluated (Built-in Mathematica Symbol)

Unevaluated[expr] represents the unevaluated form of expr when it appears as the argument to a function.

UnsameQ (Built-in Mathematica Symbol)

lhs =!= rhs yields True if the expression lhs is not identical to rhs, and yields False otherwise.

Unset (Built-in Mathematica Symbol)

lhs =. removes any rules defined for lhs.

Variables (Built-in Mathematica Symbol)

Variables[poly] gives a list of all independent variables in a polynomial.

ZeroTest (Built-in Mathematica Symbol)

ZeroTest is an option to various linear algebra functions that gives a function to use in testing whether symbolic expressions should be treated as zero.

$ExportFormats (Built-in Mathematica Symbol)

$ExportFormats gives a list of export formats currently supported in your Mathematica system.

$MinNumber (Built-in Mathematica Symbol)

$MinNumber gives the minimum positive arbitrary-precision number that can be represented on a particular computer system.

$Post (Built-in Mathematica Symbol)

$Post is a global variable whose value, if set, is applied to every output expression.

$TimeZone (Built-in Mathematica Symbol)

$TimeZone gives the current time zone to assume for dates and times.

Chini Equations (Mathematica Tutorial)

Chini equations are a generalization of Abel and Riccati equations. This solves a Chini equation.