for the i-th GAS space. The number of interspace excitations, n exc , starting from a value of zero (disconnected spaces), was gradually enlarged until convergence in total energy was reached. Local and cumulative constraints are exactly equivalent for disconnected spaces (n exc = 0), and yield very similar results for single excitations (n exc = 1). Looking at the sizes of the Hilbert spaces, as we will do later in depth, the hightest discrepancy between local and cumulative constraints is expected for n exc = 1. Since the deviation was negligible already in this case we tested only cumulative constraints for n exc > 1.