4. Consider relation R(a) containing a set of positive integers with no duplicates, and the following recursive SQL query (do not be concerned that in the SQL definition, nonlinear recursions such as this one are not required to be implemented) ITH RECURSIVE Mystery(X,Y) AS (SELECT A AS X, A AS Y FROM R) UNION SELECT m1.x, m2.Y FROM Mystery m1, Mystery m2 WHERE m2.X-m1.Y+1) SELECT MAX(Y-X) 1 FROM Mystery While the definition looks complicated, Mystery in fact computes a property of R that can be stated very succinctly. Try to determine what Mystery is computing about R, and demonstrate your understanding by identifying, from the list below, the correct example of the result returned by the above query. a) IfR- (1, 5, 9, 10, 12, 153 then the query returns 2 b) If R- 2,4, 6, 8, 103 then the query returns 0 Oc) If R- (7,9, 10, 14, 15, 16, 183 then the query returns 12 O d) If R- 1, 5, 9, 10, 12, 15) then the query returns 1