(VAR x y z)
(RULES
+(+(x, y), z) -> +(x, +(y, z))
+(0, 0) -> 0
+(x, -(x)) -> 0
f(0, y, z) -> y
g(+(x, y), y) -> f(+(x, y), x, y)
)
(COMMENT Example 3.7 in \cite{SK90})