The Word Problem for Products of Symmetric Groups

Abstract

The word problem for products of symmetric groups (WPPSG) is a well-known NP-complete problem. An input instance of this problem consists of ``specification sets'' $X_1,\ldots,X_m \seq \{1,\ldots,n\}$ and a permutation $\tau$ on $\{1,\ldots,n\}$. The sets $X_1,\ldots,X_m$ specify a subset of the symmetric group $\cS_n$ and the question is whether the given permutation $\tau$ is a member of this subset. We discuss three subproblems of WPPSG and show that they can be solved efficiently. The subproblem WPPSG$_0$ is the restriction of WPPSG to specification sets all of which are sets of consecutive integers. The subproblem WPPSG$_1$ is the restriction of WPPSG to specification sets which have the Consecutive Ones Property. The subproblem WPPSG$_2$ is the restriction of WPPSG to specification sets which have what we call the Weak Consecutive Ones Property. WPPSG$_1$ is more general than WPPSG$_0$ and WPPSG$_2$ is more general than WPPSG$_1$. But the efficient algorithms that we use for solving WPPSG$_1$ and WPPSG$_2$ have, as a sub-routine, the efficient algorithm for solving WPPSG$_0$.