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

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