Inference Rules for Mutation The local form(MUL): {e--}[e]:=e'{e-e}. The global form(MUG): {(e--)*r}[e]:=e'{(e-e)*r}. The backward-reasoning form(MUBR): {(e一-)*(e一e)-*p)}[e]:=e'{p}. One rule implies another. Inference Rules for Mutation One rule implies another