YES
LCTRS
  Theories
    Core, Ints
  Signature
    fastfib: Int -> Int
    g: Int -> Int
    u: (Int, Int, Int, Int, Int) -> Int
    v: (Int, Int, Int, Int, Int) -> Int
  Rules
    fastfib(?54) -> u(?54, 0, 1, 0, 0)
    g(?55) -> g(?55)
    u(?56, ?57, ?58, ?59, ?60) -> v(?56, ?57, ?58, ?59, g(0)) [>(?56, 1)]
    u(?61, ?62, ?63, ?64, ?65) -> 0 [<=(?61, 0)]
    u(?66, ?67, ?68, ?69, ?70) -> 1 [?66 = 1]
    v(?71, ?72, ?73, ?74, ?75) -> ?73 [>=(?72, ?71)]
    v(?76, ?77, ?78, ?79, ?80) -> v(?76, +(?77, 1), +(?78, ?79), ?78, ?80) [<(?77, ?76)]
Confluent by Orthogonality with proof:
  no critical pairs

Elapsed Time:  56.86 ms