Certification Problem

Input (TPDB TRS_Standard/Transformed_CSR_04/Ex5_DLMMU04_Z)

The rewrite relation of the following TRS is considered.

pairNs cons(0,n__incr(oddNs)) (1)
oddNs incr(pairNs) (2)
incr(cons(X,XS)) cons(s(X),n__incr(activate(XS))) (3)
take(0,XS) nil (4)
take(s(N),cons(X,XS)) cons(X,n__take(N,activate(XS))) (5)
zip(nil,XS) nil (6)
zip(X,nil) nil (7)
zip(cons(X,XS),cons(Y,YS)) cons(pair(X,Y),n__zip(activate(XS),activate(YS))) (8)
tail(cons(X,XS)) activate(XS) (9)
repItems(nil) nil (10)
repItems(cons(X,XS)) cons(X,n__cons(X,n__repItems(activate(XS)))) (11)
incr(X) n__incr(X) (12)
take(X1,X2) n__take(X1,X2) (13)
zip(X1,X2) n__zip(X1,X2) (14)
cons(X1,X2) n__cons(X1,X2) (15)
repItems(X) n__repItems(X) (16)
activate(n__incr(X)) incr(X) (17)
activate(n__take(X1,X2)) take(X1,X2) (18)
activate(n__zip(X1,X2)) zip(X1,X2) (19)
activate(n__cons(X1,X2)) cons(X1,X2) (20)
activate(n__repItems(X)) repItems(X) (21)
activate(X) X (22)

Property / Task

Prove or disprove termination.

Answer / Result

No.

Proof (by ttt2 @ termCOMP 2023)

1 Loop

The following loop proves nontermination.

t0 = pairNs
cons(0,n__incr(oddNs))
cons(0,n__incr(incr(pairNs)))
= t2
where t2 = C[t0] and C = cons(0,n__incr(incr()))