public void AssignExercise(Student student, Exercise exercise)
 {
     student.Exercises.Add(exercise);
 }
        //public List<Exercise> AssignedExercises { get; set; } = new List<Exercise>();


        //Method that accepts a student and an exercise to the student's list of assigned exercises
        public void AssignExercise(Student assignedStudent, Exercise exerciseToAssign)
        {
            assignedStudent.AssignedExercises.Add(exerciseToAssign);
            exerciseToAssign.assignedStudents.Add(assignedStudent);
        }