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

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