Consider the following relations containing airline flight information:

Flights (flno: integer, from: string, to: string, distance: integer, departs: time, arrives: time)

Aircraft (aid: integer, aname: string, cruisingrange: integer)

Certifed (eid: integer, aid: integer)

Employees (eid: integer, ename: string, salary: integer)

Note that the Employees relation describes pilots and other kinds of employees as well; every pilot is certified for some aircraft (otherwise, he or she would not qualify as a pilot), and only pilots are certified to fly.

Write the following queries in domain relational calculus.

1. Find the eids of pilots certified for some Boeing aircraft.

2. Find the names of pilots certified for some Boeing aircraft.

3. Find the names of pilots who can operate planes with a range greater than 3,000 miles but are not certified on any Boeing aircraft.

4. Identify the flights that can be piloted by every pilot whose salary is more than $100,000.

?