Fonte:
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/57221413-5547-4564-93A6-B9B575C00999/0/IVA-of%20circ%2030123.pdf
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/B294DB9C-A377-4A68-A9C6-ED7B210CB06A/0/ProcN6833%20-%202010%20-%20Ficha%20doutrinaria.pdf
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/0207781F-CD0D-4EAF-BCE4-77BB6005D99D/0/inf%201901.pdf
