(VAR x y z)
(RULES
  +(x,0)  -> x
  +(x,s(y))  -> s(+(x,y))
  +(0,y)  -> y
  +(s(x),y)  -> s(+(x,y))
  dbl(0) -> 0
  dbl(s(x))  -> s(s(dbl(x)))
  +(+(x,y),z) -> +(x,+(y,z))
  +(x,y) -> + (y,x)
  dbl(+(x,y)) -> +(dbl(x),dbl(y))
)
(COMMENT from the collection of \cite{AT2012})