(VAR x y z)
(RULES
+(a,b) -> +(b,a)
+(a,+(b,z)) -> +(b,+(a,z))
+(+(x,y),z) -> +(x,+(y,z))
f(a,y) -> a
f(b,y) -> b
f(+(x,y),z) -> +(f(x,z),f(y,z))
)
(COMMENT Example 2.8 in \cite{SK90})