I have a question about buying ticket from Gardermoen to Oslo central! I will stay in Oslo for few days, so I would like to buy one week 1 zone ticket. And I found out if I travel from Gardemrmoen, I can use supplementary ticket. So I would like to know if I can buy both of this at the airport? And where should I buy them? Does Narvesen in the airport sell one week 1 zone ticket and then I buy supplementary ticket from NSB's machine?