Certification Problem

Input (TPDB SRS_Relative/Waldmann_19/random-150)

The relative rewrite relation R/S is considered where R is the following TRS

c(b(b(x1))) → a(c(a(x1))) (1)
a(c(c(x1))) → a(a(b(x1))) (2)
a(a(c(x1))) → b(b(a(x1))) (3)

and S is the following TRS.

b(c(b(x1))) → a(b(b(x1))) (4)
a(b(b(x1))) → a(c(b(x1))) (5)
b(c(c(x1))) → c(b(b(x1))) (6)
c(c(a(x1))) → a(b(c(x1))) (7)

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by AProVE @ termCOMP 2023)

1 String Reversal

Since only unary symbols occur, one can reverse all terms and obtains the TRS
b(b(c(x1))) → a(c(a(x1))) (8)
c(c(a(x1))) → b(a(a(x1))) (9)
c(a(a(x1))) → a(b(b(x1))) (10)
b(c(b(x1))) → b(b(a(x1))) (11)
b(b(a(x1))) → b(c(a(x1))) (12)
c(c(b(x1))) → b(b(c(x1))) (13)
a(c(c(x1))) → c(b(a(x1))) (14)

1.1 Closure Under Flat Contexts

Using the flat contexts

{b(☐), c(☐), a(☐)}

We obtain the transformed TRS
b(b(b(c(x1)))) → b(a(c(a(x1)))) (15)
c(b(b(c(x1)))) → c(a(c(a(x1)))) (16)
a(b(b(c(x1)))) → a(a(c(a(x1)))) (17)
b(c(c(a(x1)))) → b(b(a(a(x1)))) (18)
c(c(c(a(x1)))) → c(b(a(a(x1)))) (19)
a(c(c(a(x1)))) → a(b(a(a(x1)))) (20)
b(c(a(a(x1)))) → b(a(b(b(x1)))) (21)
c(c(a(a(x1)))) → c(a(b(b(x1)))) (22)
a(c(a(a(x1)))) → a(a(b(b(x1)))) (23)
b(c(b(x1))) → b(b(a(x1))) (11)
b(b(a(x1))) → b(c(a(x1))) (12)
b(c(c(b(x1)))) → b(b(b(c(x1)))) (24)
c(c(c(b(x1)))) → c(b(b(c(x1)))) (25)
a(c(c(b(x1)))) → a(b(b(c(x1)))) (26)
b(a(c(c(x1)))) → b(c(b(a(x1)))) (27)
c(a(c(c(x1)))) → c(c(b(a(x1)))) (28)
a(a(c(c(x1)))) → a(c(b(a(x1)))) (29)

1.1.1 Semantic Labeling

Root-labeling is applied.

We obtain the labeled TRS
bb(bb(bc(cb(x1)))) → ba(ac(ca(ab(x1)))) (30)
bb(bb(bc(cc(x1)))) → ba(ac(ca(ac(x1)))) (31)
bb(bb(bc(ca(x1)))) → ba(ac(ca(aa(x1)))) (32)
cb(bb(bc(cb(x1)))) → ca(ac(ca(ab(x1)))) (33)
cb(bb(bc(cc(x1)))) → ca(ac(ca(ac(x1)))) (34)
cb(bb(bc(ca(x1)))) → ca(ac(ca(aa(x1)))) (35)
ab(bb(bc(cb(x1)))) → aa(ac(ca(ab(x1)))) (36)
ab(bb(bc(cc(x1)))) → aa(ac(ca(ac(x1)))) (37)
ab(bb(bc(ca(x1)))) → aa(ac(ca(aa(x1)))) (38)
bc(cc(ca(ab(x1)))) → bb(ba(aa(ab(x1)))) (39)
bc(cc(ca(ac(x1)))) → bb(ba(aa(ac(x1)))) (40)
bc(cc(ca(aa(x1)))) → bb(ba(aa(aa(x1)))) (41)
cc(cc(ca(ab(x1)))) → cb(ba(aa(ab(x1)))) (42)
cc(cc(ca(ac(x1)))) → cb(ba(aa(ac(x1)))) (43)
cc(cc(ca(aa(x1)))) → cb(ba(aa(aa(x1)))) (44)
ac(cc(ca(ab(x1)))) → ab(ba(aa(ab(x1)))) (45)
ac(cc(ca(ac(x1)))) → ab(ba(aa(ac(x1)))) (46)
ac(cc(ca(aa(x1)))) → ab(ba(aa(aa(x1)))) (47)
bc(ca(aa(ab(x1)))) → ba(ab(bb(bb(x1)))) (48)
bc(ca(aa(ac(x1)))) → ba(ab(bb(bc(x1)))) (49)
bc(ca(aa(aa(x1)))) → ba(ab(bb(ba(x1)))) (50)
cc(ca(aa(ab(x1)))) → ca(ab(bb(bb(x1)))) (51)
cc(ca(aa(ac(x1)))) → ca(ab(bb(bc(x1)))) (52)
cc(ca(aa(aa(x1)))) → ca(ab(bb(ba(x1)))) (53)
ac(ca(aa(ab(x1)))) → aa(ab(bb(bb(x1)))) (54)
ac(ca(aa(ac(x1)))) → aa(ab(bb(bc(x1)))) (55)
ac(ca(aa(aa(x1)))) → aa(ab(bb(ba(x1)))) (56)
bc(cb(bb(x1))) → bb(ba(ab(x1))) (57)
bc(cb(bc(x1))) → bb(ba(ac(x1))) (58)
bc(cb(ba(x1))) → bb(ba(aa(x1))) (59)
bb(ba(ab(x1))) → bc(ca(ab(x1))) (60)
bb(ba(ac(x1))) → bc(ca(ac(x1))) (61)
bb(ba(aa(x1))) → bc(ca(aa(x1))) (62)
bc(cc(cb(bb(x1)))) → bb(bb(bc(cb(x1)))) (63)
bc(cc(cb(bc(x1)))) → bb(bb(bc(cc(x1)))) (64)
bc(cc(cb(ba(x1)))) → bb(bb(bc(ca(x1)))) (65)
cc(cc(cb(bb(x1)))) → cb(bb(bc(cb(x1)))) (66)
cc(cc(cb(bc(x1)))) → cb(bb(bc(cc(x1)))) (67)
cc(cc(cb(ba(x1)))) → cb(bb(bc(ca(x1)))) (68)
ac(cc(cb(bb(x1)))) → ab(bb(bc(cb(x1)))) (69)
ac(cc(cb(bc(x1)))) → ab(bb(bc(cc(x1)))) (70)
ac(cc(cb(ba(x1)))) → ab(bb(bc(ca(x1)))) (71)
ba(ac(cc(cb(x1)))) → bc(cb(ba(ab(x1)))) (72)
ba(ac(cc(cc(x1)))) → bc(cb(ba(ac(x1)))) (73)
ba(ac(cc(ca(x1)))) → bc(cb(ba(aa(x1)))) (74)
ca(ac(cc(cb(x1)))) → cc(cb(ba(ab(x1)))) (75)
ca(ac(cc(cc(x1)))) → cc(cb(ba(ac(x1)))) (76)
ca(ac(cc(ca(x1)))) → cc(cb(ba(aa(x1)))) (77)
aa(ac(cc(cb(x1)))) → ac(cb(ba(ab(x1)))) (78)
aa(ac(cc(cc(x1)))) → ac(cb(ba(ac(x1)))) (79)
aa(ac(cc(ca(x1)))) → ac(cb(ba(aa(x1)))) (80)

1.1.1.1 Rule Removal

Using the linear polynomial interpretation over the naturals
[bb(x1)] = 1 · x1
[bc(x1)] = 1 · x1
[cb(x1)] = 1 · x1
[ba(x1)] = 1 · x1
[ac(x1)] = 1 · x1
[ca(x1)] = 1 · x1
[ab(x1)] = 1 · x1
[cc(x1)] = 1 + 1 · x1
[aa(x1)] = 1 · x1
all of the following rules can be deleted.
bb(bb(bc(cc(x1)))) → ba(ac(ca(ac(x1)))) (31)
cb(bb(bc(cc(x1)))) → ca(ac(ca(ac(x1)))) (34)
ab(bb(bc(cc(x1)))) → aa(ac(ca(ac(x1)))) (37)
bc(cc(ca(ab(x1)))) → bb(ba(aa(ab(x1)))) (39)
bc(cc(ca(ac(x1)))) → bb(ba(aa(ac(x1)))) (40)
bc(cc(ca(aa(x1)))) → bb(ba(aa(aa(x1)))) (41)
cc(cc(ca(ab(x1)))) → cb(ba(aa(ab(x1)))) (42)
cc(cc(ca(ac(x1)))) → cb(ba(aa(ac(x1)))) (43)
cc(cc(ca(aa(x1)))) → cb(ba(aa(aa(x1)))) (44)
ac(cc(ca(ab(x1)))) → ab(ba(aa(ab(x1)))) (45)
ac(cc(ca(ac(x1)))) → ab(ba(aa(ac(x1)))) (46)
ac(cc(ca(aa(x1)))) → ab(ba(aa(aa(x1)))) (47)
cc(ca(aa(ab(x1)))) → ca(ab(bb(bb(x1)))) (51)
cc(ca(aa(ac(x1)))) → ca(ab(bb(bc(x1)))) (52)
cc(ca(aa(aa(x1)))) → ca(ab(bb(ba(x1)))) (53)
bc(cc(cb(bb(x1)))) → bb(bb(bc(cb(x1)))) (63)
bc(cc(cb(ba(x1)))) → bb(bb(bc(ca(x1)))) (65)
cc(cc(cb(bb(x1)))) → cb(bb(bc(cb(x1)))) (66)
cc(cc(cb(bc(x1)))) → cb(bb(bc(cc(x1)))) (67)
cc(cc(cb(ba(x1)))) → cb(bb(bc(ca(x1)))) (68)
ac(cc(cb(bb(x1)))) → ab(bb(bc(cb(x1)))) (69)
ac(cc(cb(ba(x1)))) → ab(bb(bc(ca(x1)))) (71)
ba(ac(cc(cb(x1)))) → bc(cb(ba(ab(x1)))) (72)
ba(ac(cc(cc(x1)))) → bc(cb(ba(ac(x1)))) (73)
ba(ac(cc(ca(x1)))) → bc(cb(ba(aa(x1)))) (74)
ca(ac(cc(cc(x1)))) → cc(cb(ba(ac(x1)))) (76)
aa(ac(cc(cb(x1)))) → ac(cb(ba(ab(x1)))) (78)
aa(ac(cc(cc(x1)))) → ac(cb(ba(ac(x1)))) (79)
aa(ac(cc(ca(x1)))) → ac(cb(ba(aa(x1)))) (80)

1.1.1.1.1 Rule Removal

Using the matrix interpretations of dimension 2 with strict dimension 1 over the integers
[bb(x1)] =
0
1
+
2 0
0 0
· x1
[bc(x1)] =
0
1
+
2 0
0 2
· x1
[cb(x1)] =
0
0
+
2 0
0 2
· x1
[ba(x1)] =
0
0
+
2 0
0 0
· x1
[ac(x1)] =
0
1
+
2 0
0 0
· x1
[ca(x1)] =
0
0
+
2 0
0 0
· x1
[ab(x1)] =
0
0
+
2 0
0 0
· x1
[aa(x1)] =
0
0
+
2 0
0 0
· x1
[cc(x1)] =
0
0
+
1 2
0 0
· x1
all of the following rules can be deleted.
bc(cc(cb(bc(x1)))) → bb(bb(bc(cc(x1)))) (64)
ac(cc(cb(bc(x1)))) → ab(bb(bc(cc(x1)))) (70)

1.1.1.1.1.1 Rule Removal

Using the matrix interpretations of dimension 2 with strict dimension 1 over the integers
[bb(x1)] =
0
1
+
1 0
0 0
· x1
[bc(x1)] =
0
1
+
1 0
0 0
· x1
[cb(x1)] =
0
0
+
1 0
0 1
· x1
[ba(x1)] =
0
0
+
1 0
0 0
· x1
[ac(x1)] =
0
0
+
1 0
2 0
· x1
[ca(x1)] =
0
1
+
1 0
0 0
· x1
[ab(x1)] =
0
0
+
1 0
0 0
· x1
[aa(x1)] =
0
0
+
1 0
0 0
· x1
[cc(x1)] =
0
0
+
1 1
0 0
· x1
all of the following rules can be deleted.
ca(ac(cc(ca(x1)))) → cc(cb(ba(aa(x1)))) (77)

1.1.1.1.1.1.1 Rule Removal

Using the linear polynomial interpretation over the naturals
[bb(x1)] = 1 · x1
[bc(x1)] = 1 · x1
[cb(x1)] = 1 + 1 · x1
[ba(x1)] = 1 · x1
[ac(x1)] = 1 · x1
[ca(x1)] = 1 · x1
[ab(x1)] = 1 · x1
[aa(x1)] = 1 · x1
[cc(x1)] = 1 · x1
all of the following rules can be deleted.
bb(bb(bc(cb(x1)))) → ba(ac(ca(ab(x1)))) (30)
cb(bb(bc(cb(x1)))) → ca(ac(ca(ab(x1)))) (33)
cb(bb(bc(ca(x1)))) → ca(ac(ca(aa(x1)))) (35)
ab(bb(bc(cb(x1)))) → aa(ac(ca(ab(x1)))) (36)
bc(cb(bb(x1))) → bb(ba(ab(x1))) (57)
bc(cb(bc(x1))) → bb(ba(ac(x1))) (58)
bc(cb(ba(x1))) → bb(ba(aa(x1))) (59)

1.1.1.1.1.1.1.1 Rule Removal

Using the Knuth Bendix order with w0 = 1 and the following precedence and weight functions
prec(bb) = 8 weight(bb) = 3
prec(bc) = 5 weight(bc) = 1
prec(ca) = 4 weight(ca) = 4
prec(ba) = 2 weight(ba) = 2
prec(ac) = 6 weight(ac) = 2
prec(aa) = 0 weight(aa) = 3
prec(ab) = 1 weight(ab) = 4
prec(cc) = 3 weight(cc) = 1
prec(cb) = 7 weight(cb) = 1
all of the following rules can be deleted.
bb(bb(bc(ca(x1)))) → ba(ac(ca(aa(x1)))) (32)
ab(bb(bc(ca(x1)))) → aa(ac(ca(aa(x1)))) (38)
bc(ca(aa(ab(x1)))) → ba(ab(bb(bb(x1)))) (48)
bc(ca(aa(ac(x1)))) → ba(ab(bb(bc(x1)))) (49)
bc(ca(aa(aa(x1)))) → ba(ab(bb(ba(x1)))) (50)
ac(ca(aa(ab(x1)))) → aa(ab(bb(bb(x1)))) (54)
ac(ca(aa(ac(x1)))) → aa(ab(bb(bc(x1)))) (55)
ac(ca(aa(aa(x1)))) → aa(ab(bb(ba(x1)))) (56)
bb(ba(ab(x1))) → bc(ca(ab(x1))) (60)
bb(ba(ac(x1))) → bc(ca(ac(x1))) (61)
bb(ba(aa(x1))) → bc(ca(aa(x1))) (62)
ca(ac(cc(cb(x1)))) → cc(cb(ba(ab(x1)))) (75)

1.1.1.1.1.1.1.1.1 R is empty

There are no rules in the TRS. Hence, it is terminating.