PFFM and Quasi-Morishima matrices
In 1983, Greenberg  advanced an open problem “We do not have simple criterion that will enable us to characterize which elements of PFFM are quasi-Morishima and which are not.” In this paper, two algorithms of time complexity O(e) are provided.The algorithms can be used to decide which PFFM is quasi-Morishima and which is not. Here e denotes the number of edges of the researched graph. So we give an answer for the open problem.
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