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

Proof:
 Uncurry Processor:
  a() -> b()
  a() -> f3(f(),a())
  b() -> f3(f(),f3(f(),b()))
  f3(f(),f3(f(),f3(f(),b()))) -> b()
  Ground Confluence Processor:
   confluent by decision procedure.