(VAR x y z)
(RULES
   +(a,b) -> b
   +(c,a) -> a
   +(x,y) -> +(y,x)
   +(+(x,y),z) -> +(x,+(y,z))
)
(COMMENT Example 4 in Nagele/Felgenhauer/Middeldorp, CADE 2017)