Is it contrary to Article 39 of the Treaty on European Union for the Belgian tax system, at Article 155 of the CIR/92 and regardless of whether Circular No Ci.RH.331/575.420 of 12 March 2008 is applied, to have the effect that Mr Jacob's Luxembourg pensions, exempted from tax pursuant to Article 18 of the Convention concluded between Belgium and Luxembourg for the avoidance of double taxation, are taken into account for the purposes of calculating the tax payable in Belgium and used as the basis of assessment for the grant of tax advantages provided for under the CIR 92, and that those advantages, such as the tax-free allowance, long-term savings, costs paid with service vouchers, costs incurred in saving energy in the home, costs incurred in protecting the home against theft or fire, and charitable donations made by the applicant, are reduced or granted to a lesser extent than if both the applicants had income earned in Belgium and if Ms Lennertz, and not Mr Jacob, had received pensions only from Belgium?