(VAR y x)
(RULES
   +(0,y) -> y
   +(s(x),y) -> s(+(y,x))
   +(x,y) -> +(y,x)
   +(+(x,x),x) -> +(x,+(x,x))
)
(COMMENT from a collection of Aoto/Toyama, FSCD 2016)