UpValues

UpValues[f]
gives a list of transformation rules corresponding to all upvalues defined for the symbol f.

You can specify the upvalues for f by making an assignment of the form UpValues[f]=list.

Define upvalues for a symbol

These are the upvalues associated with

Define upvalues for a symbol

These are the upvalues associated with

Out[2]=

UpValues returns rules corresponding to upvalues defined for a symbol:

UpValues can be used to set the values directly:

Copy a symbol's definitions to another symbol:

HoldPattern is used to protect the rules from their own definitions:

Definition and Information display upvalues but do not return them as values:

UpValues returns a value that can be used in a program:

Evaluation of an expression involves applying matching upvalues: