Manfred Göbel Heinz Kredel Reduction of Permutation-Invariant Polynomials - A Noncommutative Case Study. 158-170 2002 175 Inf. Comput. 2 http://www.idealibrary.com/links/doi/10.1006/inco.2001.3095 db/journals/iandc/iandc175.html#GobelK02