A note on the sum-rate-distortion function of some lossy source coding   problems involving infinite-valued distortion functions
  For a number of lossy source coding problems it is shown that even if the usual single-letter sum-rate-distortion expressions may become invalid for non-infinite distortion functions, they can be approached, to any desired accuracy, via the usual valid expressions for appropriately truncated finite versions of the distortion functions. 
Prakash Ishwar
cs.IT math.IT