The derivation operator \\(g: 2^Y \rightarrow 2^X\\) is defined symmetrically.

Let \\(y \subseteq Y\\) be a subset of the attributes.

Then define \\(y' = g(y) \subseteq X\\) as the set of objects which have every attribute in \\(Y\\).

Let \\(y \subseteq Y\\) be a subset of the attributes.

Then define \\(y' = g(y) \subseteq X\\) as the set of objects which have every attribute in \\(Y\\).