The Runtime Complexity (innermost) of the given CpxTRS could be proven to be BOUNDS(n^1, INF).

(0) Obligation:

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

walk#1(Leaf(x2)) → cons_x(x2)
walk#1(Node(x5, x3)) → comp_f_g(walk#1(x5), walk#1(x3))
comp_f_g#1(comp_f_g(x4, x5), comp_f_g(x2, x3), x1) → comp_f_g#1(x4, x5, comp_f_g#1(x2, x3, x1))
comp_f_g#1(comp_f_g(x7, x9), cons_x(x2), x4) → comp_f_g#1(x7, x9, Cons(x2, x4))
comp_f_g#1(cons_x(x2), comp_f_g(x5, x7), x3) → Cons(x2, comp_f_g#1(x5, x7, x3))
comp_f_g#1(cons_x(x5), cons_x(x2), x4) → Cons(x5, Cons(x2, x4))
main(Leaf(x4)) → Cons(x4, Nil)
main(Node(x9, x5)) → comp_f_g#1(walk#1(x9), walk#1(x5), Nil)

Rewrite Strategy: INNERMOST

(1) CpxTrsToCpxRelTrsProof (BOTH BOUNDS(ID, ID) transformation)

Transformed TRS to relative TRS where S is empty.

(2) Obligation:

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

walk#1(Leaf(x2)) → cons_x(x2)
walk#1(Node(x5, x3)) → comp_f_g(walk#1(x5), walk#1(x3))
comp_f_g#1(comp_f_g(x4, x5), comp_f_g(x2, x3), x1) → comp_f_g#1(x4, x5, comp_f_g#1(x2, x3, x1))
comp_f_g#1(comp_f_g(x7, x9), cons_x(x2), x4) → comp_f_g#1(x7, x9, Cons(x2, x4))
comp_f_g#1(cons_x(x2), comp_f_g(x5, x7), x3) → Cons(x2, comp_f_g#1(x5, x7, x3))
comp_f_g#1(cons_x(x5), cons_x(x2), x4) → Cons(x5, Cons(x2, x4))
main(Leaf(x4)) → Cons(x4, Nil)
main(Node(x9, x5)) → comp_f_g#1(walk#1(x9), walk#1(x5), Nil)

S is empty.
Rewrite Strategy: INNERMOST

(3) SlicingProof (LOWER BOUND(ID) transformation)

Sliced the following arguments:
Leaf/0
cons_x/0
Cons/0

(4) Obligation:

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

walk#1(Leaf) → cons_x
walk#1(Node(x5, x3)) → comp_f_g(walk#1(x5), walk#1(x3))
comp_f_g#1(comp_f_g(x4, x5), comp_f_g(x2, x3), x1) → comp_f_g#1(x4, x5, comp_f_g#1(x2, x3, x1))
comp_f_g#1(comp_f_g(x7, x9), cons_x, x4) → comp_f_g#1(x7, x9, Cons(x4))
comp_f_g#1(cons_x, comp_f_g(x5, x7), x3) → Cons(comp_f_g#1(x5, x7, x3))
comp_f_g#1(cons_x, cons_x, x4) → Cons(Cons(x4))
main(Leaf) → Cons(Nil)
main(Node(x9, x5)) → comp_f_g#1(walk#1(x9), walk#1(x5), Nil)

S is empty.
Rewrite Strategy: INNERMOST

(5) DecreasingLoopProof (EQUIVALENT transformation)

The following loop(s) give(s) rise to the lower bound Ω(n¹):
The rewrite sequence
walk#1(Node(x5, x3)) →⁺ comp_f_g(walk#1(x5), walk#1(x3))
gives rise to a decreasing loop by considering the right hand sides subterm at position [0].
The pumping substitution is [x5 / Node(x5, x3)].
The result substitution is [ ].

(6) BOUNDS(n^1, INF)