(VAR x y)
(RULES
  f(x,h(x)) -> f(h(x),x)
  f(g(x),y) -> f(g(y),g(x))
  f(x,y) -> f(y,x)
  g(h(x)) -> h(h(x))
  h(x) -> g(x)
  g(x) -> x
)
(COMMENT from the collection of \cite{ATU2014})