For the purposes of exercising the right of deduction, are national provisions (in particular Articles 19(5) and 19-bis of Decree 633/1972 of the President of the Republic) and the practice of the national tax authorities which require that reference be had to the composition of a trader's turnover, including in order to identify so-called incidental transactions, but make no provision for a method of calculation that is based on [both] the composition and the actual destination of the acquisitions and that objectively reflects the actual share of the expenditure attributable to each of the — taxed and untaxed — activities engaged in by the taxpayer incompatible with an interpretation of Articles 168, 173, 174 and 175 of Directive 2006/112/EC which is guided by the principles of proportionality, effectiveness and neutrality, as set out in Community law?