According to this website, I'd then need to produce a test on my 1st and 7th day as well as a predeparture test. The problem is that I'll probably just get an antigen test in Luxembourg the day I leave for Brussels... so can my predeparture test be my day 1 test? The whole thing doesn't make much sense considering I'm entering from Schengen already where I'll have already been for 5 days/4 nights... I know this probably is completely unenforceable but I also want to respect the rules in place.