Certification Problem

Input (TPDB TRS_Standard/Applicative_05/ReverseLastInit)

The rewrite relation of the following TRS is considered.

app(app(app(compose,f),g),x) app(g,app(f,x)) (1)
app(reverse,l) app(app(reverse2,l),nil) (2)
app(app(reverse2,nil),l) l (3)
app(app(reverse2,app(app(cons,x),xs)),l) app(app(reverse2,xs),app(app(cons,x),l)) (4)
app(hd,app(app(cons,x),xs)) x (5)
app(tl,app(app(cons,x),xs)) xs (6)
last app(app(compose,hd),reverse) (7)
init app(app(compose,reverse),app(app(compose,tl),reverse)) (8)

Property / Task

Prove or disprove termination.

Answer / Result

Yes.

Proof (by AProVE @ termCOMP 2023)

1 Uncurrying

We uncurry the binary symbol app in combination with the following symbol map which also determines the applicative arities of these symbols.

compose is mapped to compose, compose1(x1), compose2(x1, x2), compose3(x1, x2, x3)
reverse is mapped to reverse, reverse1(x1)
reverse2 is mapped to reverse2, reverse21(x1), reverse22(x1, x2)
nil is mapped to nil
cons is mapped to cons, cons1(x1), cons2(x1, x2)
hd is mapped to hd, hd1(x1)
tl is mapped to tl, tl1(x1)
last is mapped to last
init is mapped to init


There are no uncurry rules.
No rules have to be added for the eta-expansion.

Uncurrying the rules and adding the uncurrying rules yields the new set of rules
compose3(f,g,x) app(g,app(f,x)) (19)
reverse1(l) reverse22(l,nil) (20)
reverse22(nil,l) l (21)
reverse22(cons2(x,xs),l) reverse22(xs,cons2(x,l)) (22)
hd1(cons2(x,xs)) x (23)
tl1(cons2(x,xs)) xs (24)
last compose2(hd,reverse) (25)
init compose2(reverse,compose2(tl,reverse)) (26)
app(compose,y1) compose1(y1) (9)
app(compose1(x0),y1) compose2(x0,y1) (10)
app(compose2(x0,x1),y1) compose3(x0,x1,y1) (11)
app(reverse,y1) reverse1(y1) (12)
app(reverse2,y1) reverse21(y1) (13)
app(reverse21(x0),y1) reverse22(x0,y1) (14)
app(cons,y1) cons1(y1) (15)
app(cons1(x0),y1) cons2(x0,y1) (16)
app(hd,y1) hd1(y1) (17)
app(tl,y1) tl1(y1) (18)

1.1 Rule Removal

Using the Knuth Bendix order with w0 = 1 and the following precedence and weight functions
prec(nil) = 12 weight(nil) = 1
prec(last) = 19 weight(last) = 4
prec(hd) = 3 weight(hd) = 1
prec(reverse) = 0 weight(reverse) = 2
prec(init) = 6 weight(init) = 7
prec(tl) = 15 weight(tl) = 1
prec(compose) = 9 weight(compose) = 1
prec(reverse2) = 1 weight(reverse2) = 2
prec(cons) = 17 weight(cons) = 2
prec(reverse1) = 16 weight(reverse1) = 1
prec(hd1) = 2 weight(hd1) = 1
prec(tl1) = 8 weight(tl1) = 1
prec(compose1) = 10 weight(compose1) = 1
prec(reverse21) = 14 weight(reverse21) = 1
prec(cons1) = 18 weight(cons1) = 1
prec(compose3) = 7 weight(compose3) = 1
prec(app) = 11 weight(app) = 0
prec(reverse22) = 13 weight(reverse22) = 0
prec(cons2) = 5 weight(cons2) = 0
prec(compose2) = 4 weight(compose2) = 1
all of the following rules can be deleted.
compose3(f,g,x) app(g,app(f,x)) (19)
reverse1(l) reverse22(l,nil) (20)
reverse22(nil,l) l (21)
reverse22(cons2(x,xs),l) reverse22(xs,cons2(x,l)) (22)
hd1(cons2(x,xs)) x (23)
tl1(cons2(x,xs)) xs (24)
last compose2(hd,reverse) (25)
init compose2(reverse,compose2(tl,reverse)) (26)
app(compose,y1) compose1(y1) (9)
app(compose1(x0),y1) compose2(x0,y1) (10)
app(compose2(x0,x1),y1) compose3(x0,x1,y1) (11)
app(reverse,y1) reverse1(y1) (12)
app(reverse2,y1) reverse21(y1) (13)
app(reverse21(x0),y1) reverse22(x0,y1) (14)
app(cons,y1) cons1(y1) (15)
app(cons1(x0),y1) cons2(x0,y1) (16)
app(hd,y1) hd1(y1) (17)
app(tl,y1) tl1(y1) (18)

1.1.1 R is empty

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