A functional dependency 𝐹: 𝑋 → 𝑌 is termed as a useful functional…

A functional dependency 𝐹: 𝑋 → 𝑌 is termed as a useful functional dependency if and only if it satisfies all the following three conditions: 

 • 𝑋 is not the empty set.

 • 𝑌 is not the empty set.

 • Intersection of 𝑋 and 𝑌 is the empty set. 

For a relation 𝑅 with 4 attributes, the total number of possible useful functional dependencies is ________