ly, the motion planning problem is that of computing a path between two points in the topological space FP. In the rst two of ve seminal papers on the \Piano Movers' Problem" ([220{222, 229, 223], collected in the book [131]), Schwartz and Sharir show that the boundary of FP is a semialgebraic set (assuming the original constraints of the problem are semialgebraic). This then allows the motion ...