Certification Problem

Input (TPDB SRS_Relative/Waldmann_19/random-75)

The rewrite relation of the following TRS is considered.

c(b(a(x1)))	→	a(b(b(x1)))	(1)
b(a(c(x1)))	→	b(b(b(x1)))	(2)
a(c(c(x1)))	→	a(b(b(x1)))	(3)
c(c(a(x1)))	→	c(a(c(x1)))	(4)
a(a(a(x1)))	→	a(a(b(x1)))	(5)
a(b(a(x1)))	→	b(b(a(x1)))	(6)
b(b(b(x1)))	→	a(b(c(x1)))	(7)

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by matchbox @ termCOMP 2023)

1 String Reversal

Since only unary symbols occur, one can reverse all terms and obtains the TRS

a(b(c(x1)))	→	b(b(a(x1)))	(8)
c(a(b(x1)))	→	b(b(b(x1)))	(9)
c(c(a(x1)))	→	b(b(a(x1)))	(10)
a(c(c(x1)))	→	c(a(c(x1)))	(11)
a(a(a(x1)))	→	b(a(a(x1)))	(12)
a(b(a(x1)))	→	a(b(b(x1)))	(13)
b(b(b(x1)))	→	c(b(a(x1)))	(14)

1.1 Dependency Pair Transformation

The following set of initial dependency pairs has been identified.

c^#(c(a(x1)))	→	b^#(b(a(x1)))	(15)
c^#(c(a(x1)))	→	b^#(a(x1))	(16)
c^#(a(b(x1)))	→	b^#(b(x1))	(17)
c^#(a(b(x1)))	→	b^#(b(b(x1)))	(18)
b^#(b(b(x1)))	→	c^#(b(a(x1)))	(19)
b^#(b(b(x1)))	→	b^#(a(x1))	(20)
b^#(b(b(x1)))	→	a^#(x1)	(21)
a^#(c(c(x1)))	→	c^#(a(c(x1)))	(22)
a^#(c(c(x1)))	→	a^#(c(x1))	(23)
a^#(b(c(x1)))	→	b^#(b(a(x1)))	(24)
a^#(b(c(x1)))	→	b^#(a(x1))	(25)
a^#(b(c(x1)))	→	a^#(x1)	(26)
a^#(b(a(x1)))	→	b^#(x1)	(27)
a^#(b(a(x1)))	→	b^#(b(x1))	(28)
a^#(b(a(x1)))	→	a^#(b(b(x1)))	(29)
a^#(a(a(x1)))	→	b^#(a(a(x1)))	(30)

1.1.1 Monotonic Reduction Pair Processor with Usable Rules

Using the matrix interpretations of dimension 1 with strict dimension 1 over the rationals with delta = 1

[c(x₁)]

x₁ +

[b(x₁)]

x₁ +

[a(x₁)]

x₁ +

[c^#(x₁)]

x₁ +

[b^#(x₁)]

x₁ +

[a^#(x₁)]

x₁ +

together with the usable rules

a(b(c(x1)))	→	b(b(a(x1)))	(8)
c(a(b(x1)))	→	b(b(b(x1)))	(9)
c(c(a(x1)))	→	b(b(a(x1)))	(10)
a(c(c(x1)))	→	c(a(c(x1)))	(11)
a(a(a(x1)))	→	b(a(a(x1)))	(12)
a(b(a(x1)))	→	a(b(b(x1)))	(13)
b(b(b(x1)))	→	c(b(a(x1)))	(14)

(w.r.t. the implicit argument filter of the reduction pair), the pairs

c^#(c(a(x1)))	→	b^#(a(x1))	(16)
c^#(a(b(x1)))	→	b^#(b(x1))	(17)
b^#(b(b(x1)))	→	b^#(a(x1))	(20)
b^#(b(b(x1)))	→	a^#(x1)	(21)
a^#(c(c(x1)))	→	c^#(a(c(x1)))	(22)
a^#(c(c(x1)))	→	a^#(c(x1))	(23)
a^#(b(c(x1)))	→	b^#(b(a(x1)))	(24)
a^#(b(c(x1)))	→	b^#(a(x1))	(25)
a^#(b(c(x1)))	→	a^#(x1)	(26)
a^#(b(a(x1)))	→	b^#(x1)	(27)
a^#(b(a(x1)))	→	b^#(b(x1))	(28)
a^#(a(a(x1)))	→	b^#(a(a(x1)))	(30)

and no rules could be deleted.

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 2 components.

The 1^st component contains the pair

c^#(c(a(x1)))	→	b^#(b(a(x1)))	(15)
b^#(b(b(x1)))	→	c^#(b(a(x1)))	(19)
c^#(a(b(x1)))	→	b^#(b(b(x1)))	(18)

1.1.1.1.1 Reduction Pair Processor with Usable Rules

Using the matrix interpretations of dimension 2 with strict dimension 1 over the arctic semiring over the naturals

[c(x₁)]

0	0
-2	0

· x₁ +

-∞

[b(x₁)]

0	0
-2	-2

· x₁ +

-∞

[a(x₁)]

0	0
0	0

· x₁ +

-∞

[c^#(x₁)]

1	2
1	2

· x₁ +

-∞

[b^#(x₁)]

1	1
1	1

· x₁ +

-∞

together with the usable rules

a(b(c(x1)))	→	b(b(a(x1)))	(8)
c(a(b(x1)))	→	b(b(b(x1)))	(9)
c(c(a(x1)))	→	b(b(a(x1)))	(10)
a(c(c(x1)))	→	c(a(c(x1)))	(11)
a(a(a(x1)))	→	b(a(a(x1)))	(12)
a(b(a(x1)))	→	a(b(b(x1)))	(13)
b(b(b(x1)))	→	c(b(a(x1)))	(14)

(w.r.t. the implicit argument filter of the reduction pair), the pairs

c^#(c(a(x1)))	→	b^#(b(a(x1)))	(15)
c^#(a(b(x1)))	→	b^#(b(b(x1)))	(18)

could be deleted.

1.1.1.1.1.1 Monotonic Reduction Pair Processor with Usable Rules

Using the matrix interpretations of dimension 1 with strict dimension 1 over the rationals with delta = 1

[c(x₁)]

x₁ +

[b(x₁)]

x₁ +

[a(x₁)]

x₁ +

[c^#(x₁)]

x₁ +

[b^#(x₁)]

x₁ +

together with the usable rules

a(b(c(x1)))	→	b(b(a(x1)))	(8)
c(a(b(x1)))	→	b(b(b(x1)))	(9)
c(c(a(x1)))	→	b(b(a(x1)))	(10)
a(c(c(x1)))	→	c(a(c(x1)))	(11)
a(a(a(x1)))	→	b(a(a(x1)))	(12)
a(b(a(x1)))	→	a(b(b(x1)))	(13)
b(b(b(x1)))	→	c(b(a(x1)))	(14)

(w.r.t. the implicit argument filter of the reduction pair), the pair

b^#(b(b(x1)))

→

c^#(b(a(x1)))

(19)

and no rules could be deleted.

1.1.1.1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 0 components.

The 2^nd component contains the pair

a^#(b(a(x1)))

→

a^#(b(b(x1)))

(29)

1.1.1.1.2 Reduction Pair Processor with Usable Rules

Using the matrix interpretations of dimension 3 with strict dimension 1 over the arctic semiring over the naturals

[c(x₁)]

0	0	0
-3	-3	0
-3	-3	-3

· x₁ +

-∞

[b(x₁)]

0	0	0
-3	-3	0
-3	-3	-3

· x₁ +

-∞

[a(x₁)]

0	0	0
0	0	0
0	0	0

· x₁ +

-∞

[a^#(x₁)]

2	3	3
2	3	3
2	3	3

· x₁ +

-∞

together with the usable rules

a(b(c(x1)))	→	b(b(a(x1)))	(8)
c(a(b(x1)))	→	b(b(b(x1)))	(9)
c(c(a(x1)))	→	b(b(a(x1)))	(10)
a(c(c(x1)))	→	c(a(c(x1)))	(11)
a(a(a(x1)))	→	b(a(a(x1)))	(12)
a(b(a(x1)))	→	a(b(b(x1)))	(13)
b(b(b(x1)))	→	c(b(a(x1)))	(14)

(w.r.t. the implicit argument filter of the reduction pair), the pair

a^#(b(a(x1)))

→

a^#(b(b(x1)))

(29)

could be deleted.

1.1.1.1.2.1 Dependency Graph Processor

The dependency pairs are split into 0 components.