(VAR x y z)
(RULES
   +(x,0) -> x
   -(0) -> 0
   -(-(x)) -> x
   -(+(x,y)) -> +(-(x),-(y))
   +(x,-(x)) -> 0
   +(+(x,-(x)),y) -> y
   +(+(x,y),z) -> +(x,+(y,z))
   +(x,+(y,z)) -> +(+(x,y),z)
   +(x,y) -> +(y,x)
)
(COMMENT Example 3.26 of Bachmair 1991)