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