PROLOG - conditional function

How can I list list the names of courses having both male and female students registered for them.

CODE:

/*student(name,studnumb,age,sex)*/ 
student(braum,1234,22,male).
student(lux,7839,26,female).
student(ekko,1726,29,male).
student(kayle,1114,25,female).
student(darius,6654,36,male).
student(morgana,4627,20,female).
student(ashe,2563,25,female).
student(brand,9258,30,male).

findboys(GENDER):-
   student(_, IS, SY, GENDER),
   (  var(GENDER)->true
   ;  SY = male
   ),
   takes(IS, IT),
   teaches(TN,IT),
   writeln([TN,course(IS, _)]),
   fail
;  true.

/*takes(studnum,modnum)*/  
takes(1234,1111).
takes(7839,1111).
takes(1726,1111).
takes(1114,2345).
takes(6654,1111).
takes(4627,4588).
takes(2563,2222).
takes(9258,6534).

/*course(modnum,modname)*/ 
course(2222,maths).
course(2345,english).
course(1111,computerscience).
course(6654,spanish).
course(6789,antrophormism).
course(4588,teology).

Unfortunately, I can not achieve the right query or conditional to print the list the names of courses having both male and female students registered for them

With Prolog, think of it as a logical statement:

C is a class with both male and female students if has_male_students(C) and has_female_students(C)

You can write that as follows, thinking of the :- operator as the if:

has_both_mf(C) :- has_gender(C, male), has_gender(C, female).

Now you just have to figure the logic for a class having a specific gender:

C has gender G students if C has id CourseId, student Id takes course CourseId and student Id is gender G.

You can write that as:

has_gender(C, G) :-
    course(CourseId, C),
    takes(StudentId, CourseId),
    student(_, StudentId, _, G).

Now you're going to get repeats because a class may have multiple casts of male and female students, so a given class solves the same logic in more than one way. I'll leave that as an exercise to get unique solutions. An easy way is to use the once/1 predicate in SWI Prolog (you can find it in the documentation).