We can also modify our map building operation to a more concise form by using the mapValues function:

fun getCoursesWithSubscribedStudents(): Map<Course, List<Student>> =
        getStudents()
                .flatMap { student ->
                    student.courses.map { course -> course to student }
                }
                .groupBy { (course, _) -> course }
                .mapValues { (course, courseStudentPairs) ->
                    courseStudentPairs.map { it -> it.second }
                }