Certification Problem

Input (COPS 901)

The rewrite relation of the following (conditional) TRS is considered.

The question is whether the following conditions are infeasible, i.e., there is no substitution σ such that all of the following is true:

Prove or disprove an infeasibility problem.

Yes.

add(0,x)	→	x	\|
add(s(x),y)	→	s(add(x,y))	\|
mult(0,y)	→	0	\|
mult(s(x),y)	→	add(mult(x,y),y)	\|
lte(0,y)	→	true	\|
lte(s(x),0)	→	false	\|
lte(s(x),s(y))	→	lte(x,y)	\|
minus(0,s(y))	→	0	\|
minus(x,0)	→	x	\|
minus(s(x),s(y))	→	minus(x,y)	\|
mod(0,y)	→	0	\|
mod(x,0)	→	x	\|
mod(x,s(y))	→	mod(minus(x,s(y)),s(y))	\| lte(s(y),x) ≈ true
mod(x,s(y))	→	x	\| lte(s(y),x) ≈ false
div(0,s(x))	→	0	\|
div(s(x),s(y))	→	0	\| lte(s(x),y) ≈ true
div(s(x),s(y))	→	s(div(minus(x,y),s(y)))	\| lte(s(x),y) ≈ false
power(x,0)	→	s(0)	\|
power(x,n)	→	mult(mult(power(x,div(n,s(s(0)))),power(x,div(n,s(s(0))))),s(0))	\| n ≈ s(n'), mod(n,s(s(0))) ≈ 0
power(x,n)	→	mult(mult(power(x,div(n,s(s(0)))),power(x,div(n,s(s(0))))),x)	\| n ≈ s(n'), mod(n,s(s(0))) ≈ s(z)

div(s(x),s(y))

→

s(q)

| lte(s(x),y) ≈ false, div(minus(x,y),s(y)) ≈ q

div(minus(x,y),s(y))q

power(x,n)

→

mult(mult(y,y),s(0))

| n ≈ s(n'), mod(n,s(s(0))) ≈ 0, power(x,div(n,s(s(0)))) ≈ y

power(x,div(n,s(s(0))))y

power(x,n)

→

mult(mult(y,y),x)

| n ≈ s(n'), mod(n,s(s(0))) ≈ s(z), power(x,div(n,s(s(0)))) ≈ y

power(x,div(n,s(s(0))))y

We collect the conditions in the fresh compound-symbol |.

We show non-reachability w.r.t. the underlying TRS.

Non-reachability is shown by the TCAP approximation.