The right side of an immediate definition is evaluated when the definition is made:
The right side of a delayed definition is evaluated each time the definition is used:
The arguments of the left side of a definition are evaluated before the definition is made:
Definitions with the same left side overwrite earlier ones:
The pattern variable is renamed if necessary inside a nested scope:
Delayed assignment introduces a scope that is not affected by global variables:
Immediate assignment does not introduce a scope:
Use a rule to do a transformation to a particular expression:
Use a definition to do a transformation automatically for all expressions involving
:
More specific definitions are put in front of more general ones:
Definition prints definitions associated with a symbol:
Information prints various information about a symbol, including any definitions:
DownValues returns a list of rules corresponding to any downvalues defined:
Use
Unset (
) to clear definitions with a particular left-hand side:
Clear any definitions, but not attributes:
Use
ClearAll to clear attributes, too:
, where test gives conditions for the applicability of each transformation rule. You can make several assignments with the same lhs but different forms of test. 
defines a transformation only for a literal value, rather than a function:
EXAMPLES
Basic Examples 
Scope 