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