You have to construct a telephone directory system for an organization to maintain a record of employees and their telephone numbers. Use Z-Specification language to formally specify the following functional requirements of a telephone directory system.

1. System must be able to add new employee and/or new entries
2. System must be able to remove employee and/or existing entries
3. System must be able to query the system for employee or number
4. An employee may have one or more telephone numbers
5. Some employee may not have a telephone number yet
6. A number may be shared by two or more employee.