Consider the following program.

Label the program by showing all bindings (both visible and invisible) that exist at all appropriate points in the program. What is the result of executing this program?
This example shows that the scope of a binding determines where a bound value can be accessed. However, not all bindings are necessarily visible at all points in a program. Visibility may be limited by binding two or more values to the same identifier. Many programming languages include the ability to bind the same identifier to multiple values. However, binding an identifier multiple times is not the same as updating a variable with multiple values. Bindings can be undone at a later time while variable assignment is permanent.