document: The most ambitious goal may be stated as the one of detecting the location of, say, one missing level on an otherwise complete sequence. Dyson, in a recent review [7], uses information theory concepts and argues that correlations in a sequence may provide the necessary redundancy from which error correcting codes can be constructed. At one extreme where no correlations and therefore no redundancy are present (Poissonian sequence), there is no possibility of detecting one missing level. At the other extreme, a sequence of equally spaced levels (picket fence), there is a maximum redundancy and a missed level can be obviously detected as a hole in the spectrum. Eigenvalues of random matrices, which exhibit characteristic correlations, correspond to an intermediate situation between these two extremes. The attempts to locate in the last case a single missed level have remained unsuccessful so far. However, it should be mentioned that for two-dimensional chaotic systems where, besides correlations of the order of one mean spacing as described by random matrices, the presence and the role of long range correlations governed by the shortest periodic orbits and reflected in Weyl's law describing the average spectral density, is well understood. It is then possible to approximately locate, from the study of spectral fluctuations, a single missed level [8].
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