         
     }
     
-    /// Enrolls a student
+    /**
+      Enrolls the given student.
+      - Parameter student: The student to enroll
+      - Returns: A boolean value of `true` if the student was enrolled;
+                 otherwise, `false`.
+    */
     public func enroll(student: Student) -> Bool {
         
         let enrolled: Bool

        return nil
    }
    
    /// Withdraws a student
    public func withdraw(student: Student) -> Bool {
        
        let removed: Bool

        return enrolled
    }
    
    /**
       Finds the course with give code.
       - Parameter code: The course code
       - Returns: A course object or `nil` if not found.
    */
    public func findCourse(code: String) -> Course? {
        for course in catalog {
            if course.code == code {
