Certification Problem

Input (TPDB SRS_Standard/Waldmann_07_size11/size-11-alpha-3-num-21)

The rewrite relation of the following TRS is considered.

a(x1)	→	x1	(1)
a(b(x1))	→	b(c(b(a(x1))))	(2)
b(x1)	→	a(x1)	(3)
c(c(x1))	→	x1	(4)

Property / Task

Prove or disprove termination.

Answer / Result

No.

Proof (by matchbox @ termCOMP 2023)

1 Loop

The following loop proves nontermination.

t₀	=	a(b(b(c(b(x1)))))
	→	b(c(b(a(b(c(b(x1)))))))
	→	b(c(a(a(b(c(b(x1)))))))
	→	b(c(a(b(c(b(a(c(b(x1)))))))))
	→	b(c(a(b(c(b(c(b(x1))))))))
	→	b(c(a(b(c(a(c(b(x1))))))))
	→	b(c(a(b(c(c(b(x1)))))))
	→	b(c(b(c(b(a(c(c(b(x1)))))))))
	→	b(c(a(c(b(a(c(c(b(x1)))))))))
	→	b(c(a(c(b(a(b(x1)))))))
	→	b(c(c(b(a(b(x1))))))
	→	b(b(a(b(x1))))
	→	b(b(b(c(b(a(x1))))))
	→	b(b(b(c(b(x1)))))
	→	a(b(b(c(b(x1)))))
	=	t₁₄

where t₁₄ = t₀σ and σ = {x1/x1}