public Set<BillLine> getBillLinesByStudent(Bill bill, Student student) {

		Set<BillLine> billLines = bill.getBillLines();
		Set<BillLine> billLinesByStudent = new HashSet<BillLine>();
		for (BillLine billLine : billLines) {
			if (billLine.getStudent().equals(student)) {
				billLinesByStudent.add(billLine);
			}
		}
		return billLinesByStudent;

	}