# Rule

## Rule

A link—mathematical or not—that describes a relationship between the elements of two sets. In many cases, one of these sets is an ordered sequence of numbers called ranks.

A rule is also called a mathematical law or condition.

### Examples

• The rule of a function is the expression that defines the relationship that exists between each input value (domain) of a function and the output value (range).
• An exponential rule is an expression that defines a relationship based on the exponentiation operation.
• A linear rule of the y = mx form is an expression that defines a relationship of proportionality.
• A logarithm rule is an expression that defines a relationship based on the concept of logarithm.