C-434/17: Judgment of the Court (Tenth Chamber) of 13 February 2019 (request for a preliminary ruling from the Zalaegerszegi Közigazgatási és Munkaügyi Bíróság — Hungary) — Human Operator Zrt. v Nemzeti Adó- és Vámhivatal Fellebbviteli Igazgatósága (Reference for a preliminary ruling — Harmonisation of fiscal legislation — Common system of value added tax (VAT) — Directive 2006/112/EC — Deduction of VAT — Determination of the taxable person liable for VAT — Retroactive application of a derogating measure — Principle of legal certainty)