Fonte:
http://www.dgci.min-financas.pt/NR/rdonlyres/DAD99907-7F5A-42C3-8834-A2CC811A9F14/0/circ_045_05.pdf
http://www.dgci.min-financas.pt/NR/rdonlyres/E3EA94B9-A00E-4719-BECD-05E5F5914F8C/0/circ_040_03.pdf
http://www.dgci.min-financas.pt/NR/rdonlyres/A1DEEBE8-9571-4BDD-99F4-CC2D1A6B3AFA/0/circ_023_04.pdf
