YES
LCTRS
  Theories
    Core, Ints
  Signature
    sum: Int -> Int
  Rules
    sum(?10) -> +(?10, sum(-(?10, 1))) [<=(0, -(?10, 1))]
    sum(?11) -> 0 [<=(?11, 0)]
Confluent by Orthogonality with proof:
  no critical pairs

Elapsed Time:  66.17 ms