(VAR x y z)
(RULES
   +(x,0) -> x
   +(0,x) -> x
   +(x,-(x)) -> 0
   +(x,+(-(x),y)) -> y
   -(+(x,y)) -> +(-(x),-(y))
   -(0) -> 0
   -(-(x)) -> x
   +(+(x,y),z) -> +(x,+(y,z))
   +(x,+(y,z)) -> +(y,+(x,z))
   +(x,y) -> +(y,x)
)
(COMMENT Example 4.14 of Bachmair 1991)