Fonte:
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/07DBD11D-A699-4452-8F8D-FA0A1E0D5920/0/Circ_19.pdf
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/9DD2AEF2-C09E-4261-BECF-845DDF39F4A2/0/Circ_20.pdf
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/86325CAD-40D8-4DD6-B1BE-B095AEF10B26/0/Circ_21.pdf
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/DC3340C7-2504-4B07-B61A-098EEEA10292/0/Circ_22.pdf
