S1 and S2 two Score table
here.$\ni S1\in marks$ means marks of student S1.
$not\ni S1\in marks=\vee marks=$all student marks
$e_{2}$ student table which contain city of student.
Now, in this query S1 is one or some student, S2 is all those students whose marks greater than or equal to marks of S1 and lives in Mumbai.
The student who got more than or equal to marks of some student in Mumbai.