fact: Definition mul x y := match x, y with | Pos nx, Pos ny => Pos (NN.mul nx ny) | Pos nx, Neg ny => Neg (NN.mul nx ny) | Neg nx, Pos ny => Neg (NN.mul nx ny) | Neg nx, Neg ny => Pos (NN.mul nx ny) end.
imports: ZArith Lia BigNumPrelude NSig ZSig