Given an instance of the STUDENTS relation as shown below:

For (StudentName, StudentAge) to be a key for this instance, the value $$X$$ should NOT be equal to ________.

The maximum number of superkeys for the relation schema $$R(E, F, G, H)$$ with $$E$$ as key is ______.

Consider the equation $${\left( {123} \right)_5} = {\left( {x8} \right)_y}$$ with $$x$$ and $$y$$ as unknown. The number of possible solutions is _________.

The dual of a Boolean function $$F\left( {{x_1},{x_2},\,....,\,{x_n},\, + , \cdot ,'} \right),$$ written as $${F^D}$$, is the same expression as that of $$F$$ with $$+$$ and $$ \cdot $$ swapped. $$F$$ is said to be self-dual if $$F = {F^D} \cdot $$. The number of self-dual functions with $$n$$ Boolean variables is