Problem:
 c() -> f(c())
 c() -> c()
 f(a()) -> b()
 a() -> c()

Proof:
 Uncurry Processor:
  c() -> f4(f(),c())
  c() -> c()
  f4(f(),a()) -> b()
  a() -> c()
  Ground Confluence Processor:
   non-confluent by decision procedure.