Irish bouzouki Dónal Lunny, who replaced the octave strings on the two lower G and D courses with unison strings, thus reinforcing their lower frequencies. Soon after, on a visit with Irvine to the workshop of luthier Peter Abnett, Lunny commissioned a bouzouki to the specifications of a classic, 4-course Greek bouzouki but with unison strings and a three-piece, partially staved back. Since then, the instrument has been adapted for Irish traditional and other styles of folk music. The original Greek bouzouki was a three course/six-string instrument ("trichordo"). In the 1950s, a four course/eight-string ("tetrachordo") version was developed. The newer "tetrachordo" bouzouki
Shannon capacity of a graph eight neighbors, the eight strings that it can be confused with. A subset of length-two strings forms a code with no possible confusion if and only if it corresponds to an independent set of this graph. The set of code words {"11", "23", "35", "54", "42"} forms one of these independent sets, of maximum size. If "G" is a graph representing the signals and confusable pairs of a channel, then the graph representing the length-two codewords and their confusable pairs is "G" ⊠ "G", where the symbol "⊠" represents the strong product of graphs. This is a graph that has