(0) Obligation:

Runtime Complexity Relative TRS:
The TRS R consists of the following rules:

mergesort(Cons(x', Cons(x, xs))) → splitmerge(Cons(x', Cons(x, xs)), Nil, Nil)
mergesort(Cons(x, Nil)) → Cons(x, Nil)
merge(Cons(x', xs'), Cons(x, xs)) → merge[Ite](<=(x', x), Cons(x', xs'), Cons(x, xs))
merge(Cons(x, xs), Nil) → Cons(x, xs)
splitmerge(Cons(x, xs), xs1, xs2) → splitmerge(xs, Cons(x, xs2), xs1)
splitmerge(Nil, xs1, xs2) → merge(mergesort(xs1), mergesort(xs2))
mergesort(Nil) → Nil
merge(Nil, xs2) → xs2
notEmpty(Cons(x, xs)) → True
notEmpty(Nil) → False
goal(xs) → mergesort(xs)

The (relative) TRS S consists of the following rules:

<=(S(x), S(y)) → <=(x, y)
<=(0, y) → True
<=(S(x), 0) → False
merge[Ite](False, xs1, Cons(x, xs)) → Cons(x, merge(xs1, xs))
merge[Ite](True, Cons(x, xs), xs2) → Cons(x, merge(xs, xs2))

Rewrite Strategy: INNERMOST

(1) DecreasingLoopProof (EQUIVALENT transformation)

The following loop(s) give(s) rise to the lower bound Ω(n1):
The rewrite sequence
merge(Cons(0, xs'), Cons(x, xs)) →+ Cons(0, merge(xs', Cons(x, xs)))
gives rise to a decreasing loop by considering the right hand sides subterm at position [1].
The pumping substitution is [xs' / Cons(0, xs')].
The result substitution is [ ].

(2) BOUNDS(n^1, INF)