begin
p: 1 2
p: 1 3
p: 2 2
p: 2 3
p: 3 2
p: 3 3
p: 4 2
p: 4 3
after: 4 3
after: 4 2
after: 3 3
after: 3 2
after: 2 3
after: 2 2
after: 1 3
after: 1 2
done