1. A system for assisting a program designer to remove program errors of a concurrent program, said system comprising: division means for dividing each process of a first concurrent program, consisting of a plurality of processes, into a plurality of sections; generation means for generating a network structure, consisting of nodes and arrows, which represents a set of possible execution orders of said sections of said first concurrent program, where each arrow indicates a section, and a path of said network structure indicates a possible execution order of said sections; selection means for selecting sections represented by said arrows at each branch of said network structure; and conversion means for converting said first concurrent program to a second concurrent program which executes selected execution orders consisting of said selected sections of said first concurrent program selected by said selection means and does not execute sections which are not selected.