In the case of Komar mass, we can express the mass as an integral of ##\rho + 3P##, so we can meaningful divide the total mass (or energy) of a system into the contribution due to each part, just by integrating over that spatial part of the system. What happens if we try to do this with other definitions of mass, say the ADM or Bondi mass? My overall impression is that it can't be done, but I don't have a specific reference for this, so I want to be cautious about saying it cant be done. I suppose I'm open to general ways of partitioning the mass, and not just my suggested approach of integrating some (pseudo) tensor of some sort over a spatial region. One obstacle that comes to mind with psuedotensors is the obvious issue of the gauge degree of freedom affecting the subdivision process. But this seems lacking as a proof of impossibility, at least without an example illustrating different "partitioning".