 This notion of Algorithmic Information Theory was invented independently somewhat later separately by Kolmogorov (1965) and Chaitin (1969). Levin (1974) developed a mathematical expression of the universal a priori probability as a universal (that is, maximal) lower semicomputable semimeasure M, and showed that the negative logarithm of \(M(x)\) coincides with the Kolmogorov complexity of x up to an additive logarithmic term. The actual definition of the complexity measure is: 