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