Conditional Kolmogorov Complexity and Universal Probability
  The Coding Theorem of L.A. Levin connects unconditional prefix Kolmogorov complexity with the discrete universal distribution. There are conditional versions referred to in several publications but as yet there exist no written proofs in English. Here we provide those proofs. They use a different definition than the standard one for the conditional version of the discrete universal distribution. Under the classic definition of conditional probability, there is no conditional version of the Coding Theorem. 
Paul M. B. Vitanyi (CWI and University of Amsterdam)
cs.IT math.IT