[ALPS-users] Question about CONSERVED_QUANTUMNUMBERS in DMRG code

Dear all ALPS users, I have following questions to the DMRG tutorials. Why there is N in a line: 'CONSERVED_QUANTUMNUMBERS' : 'N,Sz', I understand that Sz stands for conserved quantum number but spin model on the open chain lattice does not have quantum number called N. Is this N added to 'CONSERVED_QUANTUMNUMBERS' just in case someone may use some bosonic model? Bests, Rafał