Fourth Normal Form (4NF)
A relation schema R is in 4NF with respect to a set of dependencies F, if for every non-trivial functional dependency X ->> Y, X is a candidate key for R.
Consider the relation scheme Employee (E#, Ename, Project, Dependant)
E# -> Ename, E# ->> Project, E# ->> Dependant
Employee is not 4NF, since E# is not a candidate key for Employee