Fonte:
http://www.portaldasfinancas.gov.pt/pt/home.action#
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/2A7625C8-1189-4A83-8351-E9AF0204C8F2/0/OficCirc_90014.pdf
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/37EEA8D4-0686-4188-8E93-1B1A4C9F9E92/0/Circ_2_2010.pdf
