Elementary key normal form (EKNF) is a subtle enhancement on third normal form, thus EKNF tables are in 3NF by definition.
This happens when there is more than one unique compound key and they overlap.
Such cases can cause redundant information in the overlapping column(s).
EKNF was defined by Carlo Zaniolo in 1982.
[1] A table is in EKNF if and only if all its elementary functional dependencies begin at whole keys or end at elementary key attributes.