19. The apparatus of claim 18 , wherein the LD and LD/OCR-Key trellises are traversed by more than one path to all possible paths, wherein the traversing the LD and the LD/OCR-Key trellises comprises a step-by-step registering of an LD and an LD/OCR-Key trellis step error at each step.
19. The apparatus of claim 18 , wherein the LD and LD/OCR-Key trellises are traversed by more than one path to all possible paths, wherein the traversing the LD and the LD/OCR-Key trellises comprises a step-by-step registering of an LD and an LD/OCR-Key trellis step error at each step. 20. The apparatus of claim 19 , wherein a sequential collection of LD and LD/OCR-Key trellis step errors comprises an LD and an LD/OCR-Key critical path, wherein the critical path is a minimum error path.