, EXPLOITATION OF PROSTITUTION , THE KEEPING OF A DISORDERLY HOUSE OR BROTHEL AND LIVING ON IMMORAL EARNINGS . IT PROVIDES THAT SUPPLEMENTARY REGULATIONS MAY BE ADOPTED BY MUNICIPAL COUNCILS , PROVIDED THAT THEIR PURPOSE IS TO UPHOLD PUBLIC MORALITY OR TO ENSURE THE KEEPING OF THE PUBLIC PEACE . THE POLICE REGULATION OF THE CITY OF LIEGE OF 25 MARCH 1957 AND SUBSEQUENT ORDERS PROVIDE THAT PERSONS ENGAGED IN PROSTITUTION MAY NOT DISPLAY THEMSELVES TO PASSERS-BY , THAT THE DOORS AND WINDOWS OF THE PREMISES WHERE THEY PURSUE THEIR ACTIVITY ARE TO BE CLOSED AND COVERED SO THAT IT IS IMPOSSIBLE TO SEE INSIDE AND THAT THOSE PERSONS MAY NOT STAND IN THE STREET NEAR SUCH PREMISES .
4 THE QUESTIONS SUBMITTED BY THE NATIONAL COURT , THE WORDING OF WHICH IS PRACTICALLY IDENTICAL IN BOTH CASES , HAVE BEEN DIVIDED BY THE COURT MAKING THE REFERENCE INTO TWO GROUPS , ENTITLED ' ' THE CONCEPT OF PUBLIC POLICY ' ' AND ' ' PROCEDURAL SAFEGUARDS ' ' . IN VIEW OF THE FACT THAT THE QUESTIONS IN THE TWO CASES ARE ALMOST IDENTICAL , IT IS APPROPRIATE TO JOIN THE CASES FOR THE PURPOSE OF THE JUDGMENT .
I - THE CONCEPT OF PUBLIC POLICY
QUESTIONS 1 TO 9 , 11 AND 12
5 QUESTIONS 1 TO 9 , 11 AND 12 ARE ESSENTIALLY CONCERNED WITH THE QUESTION WHETHER A MEMBER STATE MAY , BY VIRTUE OF THE RESERVATIONS CONTAINED IN ARTICLES 48 AND 56 OF THE EEC TREATY , EXPEL FROM ITS TERRITORY A NATIONAL OF ANOTHER MEMBER STATE OR DENY HIM ACCESS TO THAT TERRITORY BY REASON OF ACTIVITIES WHICH , WHEN ATTRIBUTABLE TO THE FORMER STATE ' S OWN NATIONALS , DO NOT GIVE RISE TO REPRESSIVE MEASURES .
6 THOSE QUESTIONS ARE MOTIVATED BY THE FACT THAT PROSTITUTION AS SUCH IS NOT PROHIBITED BY BELGIAN LEGISLATION , ALTHOUGH THE LAW DOES PROHIBIT CERTAIN INCIDENTAL ACTIVITIES , WHICH ARE PARTICULARLY HARMFUL FROM THE SOCIAL POINT OF VIEW , SUCH AS THE EXPLOITATION OF PROSTITUTION BY THIRD PARTIES AND VARIOUS FORMS OF INCITEMENT TO DEBAUCHERY .
7 THE RESERVATIONS CONTAINED IN ARTICLES 48 AND 56 OF THE EEC TREATY PERMIT MEMBER STATES TO ADOPT , WITH RESPECT TO THE NATIONALS OF OTHER MEMBER STATES AND ON THE GROUNDS SPECIFIED IN THOSE PROVISIONS , IN PARTICULAR GROUNDS JUSTIFIED BY THE REQUIREMENTS OF PUBLIC POLICY , MEASURES WHICH THEY CANNOT APPLY TO THEIR OWN NATIONALS , INASMUCH AS THEY HAVE NO AUTHORITY TO EXPEL THE LATTER FROM THE NATIONAL TERRITORY OR TO DENY THEM ACCESS THERETO . ALTHOUGH THAT DIFFERENCE OF TREATMENT , WHICH BEARS UPON THE NATURE OF THE MEASURES AVAILABLE , MUST THEREFORE BE ALLOWED , IT MUST NEVERTHELESS BE STRESSED THAT , IN A MEMBER STATE , THE AUTHORITY EMPOWERED TO ADOPT SUCH MEASURES MUST NOT BASE THE EXERCISE OF ITS POWERS ON ASSESSMENTS OF CERTAIN CONDUCT WHICH WOULD HAVE THE EFFECT OF APPLYING AN ARBITRARY DISTINCTION TO THE DETRIMENT OF NATIONALS OF OTHER MEMBER