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| | Even and odd permutations (Site not responding. Last check: 2007-09-10) |
 | | [The reason: if σ is even, then (12)σ is odd; if σ is odd, then (12)σ is even; the two maps are inverse to each other.] A cycle is even if and only if its length is odd. |
 | | Every permutation can be produced by a sequence of transpositions: with the first transposition we put the first element of the permutation in its proper place, the second transposition puts the second element right etc. Every transposition can be written as a product of an odd number of transpositions of adjacent elements, e.g. |
 | | Now if we compose σ with the transposition (''i'', i+1) of two adjacent numbers, then, compared to σ, the new permutation σ(''i'', i+1) will have exactly one inversion pair less (in case (''i'',''i''+1) was an inversion pair for σ) or more (in case (''i'', i+1) was not an inversion pair). |
| even-and-odd-permutations.kiwiki.homeip.net (960 words) |
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