YES
LCTRS
  Theories
    Core, Ints
  Signature
    fib: Int -> Int
  Rules
    fib(?14) -> +(fib(-(?14, 1)), fib(-(?14, 2))) [>=(-(?14, 2), 0)]
    fib(?15) -> 0 [<=(?15, 0)]
    fib(?16) -> 1 [?16 = 1]
Confluent by Orthogonality with proof:
  no critical pairs

Elapsed Time:  64.16 ms