(VAR x)
(RULES
  b(x) -> c(d(x))
  d(x) -> c(b(x))
  c(x) -> b(d(x))
  b(x) -> c(d(x))
  a(x) -> a(b(x))
  a(x) -> b(c(x))
)
(COMMENT
submitted by: Johannes Waldmann
secret problem 2019
category: SRS
)