(RULES
  a -> b
  a -> f(a)
  b -> f(f(b))
  f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(
  f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(f(
  b
  )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) -> b
)
(COMMENT
doi:10.4230/LIPIcs.RTA.2012.165
[37] Section 4 (R_64)
)