(VAR x y z)
(RULES
   +(0,x) -> x
   +(-(x),x) -> 0
   +(+(x,y),z) -> +(x,+(y,z))
   +(x,y) -> +(y,x)
   -(0) -> 0
   -(-(x)) -> x
   -(+(x,y)) -> +(-(x),-(y))
   *(1,x) -> x
   *(x,+(y,z)) -> +(*(x,y),*(x,z))
   *(*(x,y),z) -> *(x,*(y,z))
   *(x,y) -> *(y,x)
   *(x,0) -> 0
   *(x,-(y)) -> -(*(x,y))
)
(COMMENT Theory of Commutative Ring with Unit from \cite{PS81})