[ALPS-users] non-standard constraint: "NL + nR" value="N_total"

Dear All, I want to define a model for boson-boson mixture to be run by a worm code. I have two types of bosons: of type L and type R. I would like to be able to consider a conservation of total number of bosons that is : nL + nR = const. What should I put into "contraint": <CONSTRAINT quantumnumber="N" value="N_total"/> ? I would like to have something like <CONSTRAINT quantumnumber="NL + nR" value="N_total"/> An option is probably to redefine quantum numbers from: nR and nL into nA and nB by nA = (nR + nL) and nB = (nL-nR) (now nA is >=0 and nB is arbitrary) of course one would have to change creation and annihilation operators, all observables... this i why I would like to avoid it. Regards, Mateusz Łącki