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