MAYBE
LCTRS
  Theories
    Core, Ints
  Sorts
    Unit
  Signature
    fastfib: Int -> Unit
    return: Int -> Unit
    u: (Int, Int, Int, Int, Int) -> Unit
    v: (Int, Int, Int, Int, Int) -> Unit
  Rules
    v(!n, !pre1, !pre2, !val, !i) -> return(!val) [and(not(<=(!i, !n)), not(<(!val, 0)))]
    v(!n, !pre1, !pre2, !val, !i) -> return(-1) [and(not(<=(!i, !n)), <(!val, 0))]
    v(!n, !pre1, !pre2, !val, !i) -> v(!n, +(!pre1, !pre2), !pre1, +(!pre1, !pre2), +(!i, 1)) [<=(!i, !n)]
    u(!n, !pre1, !pre2, !val, !i) -> v(!n, !pre1, !pre2, !val, 2) [and(not(<=(!n, 0)), not(!n = 1))]
    u(!n, !pre1, !pre2, !val, !i) -> return(1) [and(not(<=(!n, 0)), !n = 1)]
    u(!n, !pre1, !pre2, !val, !i) -> return(0) [<=(!n, 0)]
    fastfib(!n) -> u(!n, 1, 0, 0, !rnd)
No termination info given.

Elapsed Time:  48.09 ms