cartan matrix :
   2  -1
  -3   2

root basis :
  -1   2
   0   1

coroot basis :
  -2   1
   1   0

positive roots :
[-1,0]
[-1,1]
[0,1]
[1,1]
[1,2]
[2,1]

positive coroots :
[-2,1]
[-1,1]
[-1,2]
[1,1]
[0,1]
[1,0]