@0 a = 0
@1 a = 1
@2 a = 2
@3 a = 3
@4 a = 4
@5 b = 5
@6 b = 6
@7 b = 7
@8 b = 8
@9 b = 9
@10 b = 10
@15 b = 15
@16 b = 16
@17 b = 17
@18 b = 18
@19 b = 19
@20 b = 20