??so... consider this "localization" left exact left adjoint from N-sets to Z-sets ... ??so i guess that part of the point is that it's _not_ a right adjoint ... ??or something ?? ...

??something about ... N-Z-biaction ... ???not having adjoint, though sort of coming close ?? ... ???or something ??? ....

???something about ... ???flat vs ... ??projective or something??? ... here ... ???or what ????....

??hmmm, so what _about_ something "finitary vs infinitary flatness" (or something ...??...) here ??? .... and so forth ... ???....

??... ask todd about some of this ... ??something about "cartesian bicategory" (or something...) and so forth ... ???....