The Runtime Complexity (full) of the given CpxTRS could be proven to be BOUNDS(n^2, INF).

(0) Obligation:

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

sqr(0) → 0
sqr(s(x)) → +(sqr(x), s(double(x)))
double(0) → 0
double(s(x)) → s(s(double(x)))
+(x, 0) → x
+(x, s(y)) → s(+(x, y))
sqr(s(x)) → s(+(sqr(x), double(x)))

Rewrite Strategy: FULL

(1) DecreasingLoopProof (EQUIVALENT transformation)

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

(2) BOUNDS(n^1, INF)

(3) RenamingProof (EQUIVALENT transformation)

Renamed function symbols to avoid clashes with predefined symbol.

(4) Obligation:

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

sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

S is empty.
Rewrite Strategy: FULL

(5) TypeInferenceProof (BOTH BOUNDS(ID, ID) transformation)

Infered types.

(6) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

(7) OrderProof (LOWER BOUND(ID) transformation)

Heuristically decided to analyse the following defined symbols:
sqr, +', double

They will be analysed ascendingly in the following order:
+' < sqr
double < sqr

(8) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

The following defined symbols remain to be analysed:
+', sqr, double

They will be analysed ascendingly in the following order:
+' < sqr
double < sqr

(9) RewriteLemmaProof (LOWER BOUND(ID) transformation)

Proved the following rewrite lemma:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)

Induction Base:
+'(gen_0':s2_0(a), gen_0':s2_0(0)) →_R^Ω(1)
gen_0':s2_0(a)

Induction Step:
+'(gen_0':s2_0(a), gen_0':s2_0(+(n4_0, 1))) →_R^Ω(1)
s(+'(gen_0':s2_0(a), gen_0':s2_0(n4_0))) →_IH
s(gen_0':s2_0(+(a, c5_0)))

We have rt ∈ Ω(n¹) and sz ∈ O(n). Thus, we have irc_R ∈ Ω(n).

(10) Complex Obligation (BEST)

(11) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Lemmas:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

The following defined symbols remain to be analysed:
double, sqr

They will be analysed ascendingly in the following order:
double < sqr

(12) RewriteLemmaProof (LOWER BOUND(ID) transformation)

Proved the following rewrite lemma:
double(gen_0':s2_0(n457_0)) → gen_0':s2_0(*(2, n457_0)), rt ∈ Ω(1 + n457₀)

Induction Base:
double(gen_0':s2_0(0)) →_R^Ω(1)
0'

Induction Step:
double(gen_0':s2_0(+(n457_0, 1))) →_R^Ω(1)
s(s(double(gen_0':s2_0(n457_0)))) →_IH
s(s(gen_0':s2_0(*(2, c458_0))))

We have rt ∈ Ω(n¹) and sz ∈ O(n). Thus, we have irc_R ∈ Ω(n).

(13) Complex Obligation (BEST)

(14) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Lemmas:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)
double(gen_0':s2_0(n457_0)) → gen_0':s2_0(*(2, n457_0)), rt ∈ Ω(1 + n457₀)

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

The following defined symbols remain to be analysed:
sqr

(15) RewriteLemmaProof (LOWER BOUND(ID) transformation)

Proved the following rewrite lemma:
sqr(gen_0':s2_0(n693_0)) → gen_0':s2_0(*(n693_0, n693_0)), rt ∈ Ω(1 + n693₀ + n693₀²)

Induction Base:
sqr(gen_0':s2_0(0)) →_R^Ω(1)
0'

Induction Step:
sqr(gen_0':s2_0(+(n693_0, 1))) →_R^Ω(1)
+'(sqr(gen_0':s2_0(n693_0)), s(double(gen_0':s2_0(n693_0)))) →_IH
+'(gen_0':s2_0(*(c694_0, c694_0)), s(double(gen_0':s2_0(n693_0)))) →_L^{Ω(1 + n693₀)}
+'(gen_0':s2_0(*(n693_0, n693_0)), s(gen_0':s2_0(*(2, n693_0)))) →_L^{Ω(2 + 2·n693₀)}
gen_0':s2_0(+(+(*(2, n693_0), 1), *(n693_0, n693_0)))

We have rt ∈ Ω(n²) and sz ∈ O(n). Thus, we have irc_R ∈ Ω(n²).

(16) Complex Obligation (BEST)

(17) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Lemmas:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)
double(gen_0':s2_0(n457_0)) → gen_0':s2_0(*(2, n457_0)), rt ∈ Ω(1 + n457₀)
sqr(gen_0':s2_0(n693_0)) → gen_0':s2_0(*(n693_0, n693_0)), rt ∈ Ω(1 + n693₀ + n693₀²)

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

No more defined symbols left to analyse.

(18) LowerBoundsProof (EQUIVALENT transformation)

The lowerbound Ω(n²) was proven with the following lemma:
sqr(gen_0':s2_0(n693_0)) → gen_0':s2_0(*(n693_0, n693_0)), rt ∈ Ω(1 + n693₀ + n693₀²)

(19) BOUNDS(n^2, INF)

(20) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Lemmas:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)
double(gen_0':s2_0(n457_0)) → gen_0':s2_0(*(2, n457_0)), rt ∈ Ω(1 + n457₀)
sqr(gen_0':s2_0(n693_0)) → gen_0':s2_0(*(n693_0, n693_0)), rt ∈ Ω(1 + n693₀ + n693₀²)

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

No more defined symbols left to analyse.

(21) LowerBoundsProof (EQUIVALENT transformation)

The lowerbound Ω(n²) was proven with the following lemma:
sqr(gen_0':s2_0(n693_0)) → gen_0':s2_0(*(n693_0, n693_0)), rt ∈ Ω(1 + n693₀ + n693₀²)

(22) BOUNDS(n^2, INF)

(23) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Lemmas:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)
double(gen_0':s2_0(n457_0)) → gen_0':s2_0(*(2, n457_0)), rt ∈ Ω(1 + n457₀)

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

No more defined symbols left to analyse.

(24) LowerBoundsProof (EQUIVALENT transformation)

The lowerbound Ω(n¹) was proven with the following lemma:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)

(25) BOUNDS(n^1, INF)

(26) Obligation:

TRS:
Rules:
sqr(0') → 0'
sqr(s(x)) → +'(sqr(x), s(double(x)))
double(0') → 0'
double(s(x)) → s(s(double(x)))
+'(x, 0') → x
+'(x, s(y)) → s(+'(x, y))
sqr(s(x)) → s(+'(sqr(x), double(x)))

Types:
sqr :: 0':s → 0':s
0' :: 0':s
s :: 0':s → 0':s
+' :: 0':s → 0':s → 0':s
double :: 0':s → 0':s
hole_0':s1_0 :: 0':s
gen_0':s2_0 :: Nat → 0':s

Lemmas:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)

Generator Equations:
gen_0':s2_0(0) ⇔ 0'
gen_0':s2_0(+(x, 1)) ⇔ s(gen_0':s2_0(x))

No more defined symbols left to analyse.

(27) LowerBoundsProof (EQUIVALENT transformation)

The lowerbound Ω(n¹) was proven with the following lemma:
+'(gen_0':s2_0(a), gen_0':s2_0(n4_0)) → gen_0':s2_0(+(n4_0, a)), rt ∈ Ω(1 + n4₀)

(28) BOUNDS(n^1, INF)