LE, and SCRATCHPAD II) support polynomial decomposition for purposes such as this. Barton and Zippel [2, 3] present two decomposition algorithms. Some simpli cations are suggested by Alagar and Thanh =-=[1]-=-. All these algorithms require K to be a eld of characteristic 0, they all use polynomial factorization, and they all take exponential time in the degree of f in the worst case. No decomposition algor