TRS:
 {       D(t()) -> 1(),
  D(constant()) -> 0(),
     D(+(x, y)) -> +(D(x), D(y)),
     D(*(x, y)) -> +(*(y, D(x)), *(x, D(y))),
     D(-(x, y)) -> -(D(x), D(y))}
 MPO:
  Prec:
   D > -, 
   D > *, 
   D > +, 
   constant > 0
   t ~ 1
  Strict:
   {}
   Weak:
    {}
  Qed