++++ Tax provisions - Harmonization of legislation - Turnover tax - Common system of value-added tax - Taxable persons - Bodies governed by public law - Exclusion of activities pursued as public authorities - Concept - Liability to tax where there are distortions of competition and economic activities which are important and not carried on on a negligible scale - Scope - Transposition of corresponding criteria into national law - Member States' obligations ( Council Directive 77/388, Art . 4(5 ) )