Given the following $($normalized$)$ relational model $($primary keys underlined; foreign keys in italics$)$:

EMPLOYEE$($SSN$,$ ENAME, EADDRESS, SEX, DATE$\_$OF$\_$BIRTH, SUPERVISOR, DNR$)$ SUPERVISOR: foreign key, refers to SSN in EMPLOYEE, NULL value not allowed DNR: foreign key, refers to DNR in DEPARTMENT, NULL value not allowed

DEPARTMENT$($DNR$,$ DNAME, DLOCATION, MGNR$)$

MGNR: foreign key, refers to SSN in EMPLOYEE, NULL value not allowed

PROJECT$($PNR$,$ PNAME, PDURATION, DNR$)$

DNR: foreign key, refers to DNR in DEPARTMENT, NULL value not allowed

WORKS$\_$ON$($SSN$,$ PNR$,$ HOURS$)$

SSN: foreign key, refers to SSN in EMPLOYEE, NULL value not allowed

PNR: foreign key, refers to PNR in PROJECT, NULL value not allowed

Which statement is NOT CORRECT?

Every project is always assigned to exactly one department.

Every employee must be always supervised by exactly one other employee.

An employee must work in the same department than he$/$she manages.

A department has always exactly one manager.