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

Proof:
 Uncurry Processor:
  b() -> a()
  b() -> c()
  c() -> b()
  c() -> d()
  Church Rosser Transformation Processor:
   b() -> a()
   b() -> c()
   c() -> b()
   c() -> d()
   critical peaks: joinable
   Qed