++++ 1 . Free movement of goods - Trade with non-member countries - Inward processing arrangements - Triangular operations authorized by the national authorities after consultation with the Commission - Failure to levy intra-Community monetary compensatory amounts - Subsequent challenge by the Commission on the ground that traders had obtained an unjustified advantage - Not permissible ( Commission Directive 75/349, Art . 4 ) 2 . Community law - Principles - Legal certainty - Rules imposing charges - Requirement of clarity and precision