(VAR x y z)
(RULES
  f(f(x,y),z) -> f(x,f(y,z))
  f(1,x) -> x
)
(COMMENT
doi:10.1017/CBO9781139172752
[4] Exercise 6.5(e)
submitted by: Takahito Aoto, Junichi Yoshida, and Yoshihito Toyama
)