Certification Problem

Input (TPDB TRS_Standard/AotoYamada_05/014)

The rewrite relation of the following TRS is considered.

app(app(plus,0),y) y (1)
app(app(plus,app(s,x)),y) app(s,app(app(plus,x),y)) (2)
app(app(times,0),y) 0 (3)
app(app(times,app(s,x)),y) app(app(plus,app(app(times,x),y)),y) (4)
app(app(map,f),nil) nil (5)
app(app(map,f),app(app(cons,x),xs)) app(app(cons,app(f,x)),app(app(map,f),xs)) (6)
inc app(map,app(plus,app(s,0))) (7)
double app(map,app(times,app(s,app(s,0)))) (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.

plus is mapped to plus, plus1(x1), plus2(x1, x2)
0 is mapped to 0
s is mapped to s, s1(x1)
times is mapped to times, times1(x1), times2(x1, x2)
map is mapped to map, map1(x1), map2(x1, x2)
nil is mapped to nil
cons is mapped to cons, cons1(x1), cons2(x1, x2)
inc is mapped to inc
double is mapped to double


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
plus2(0,y) y (18)
plus2(s1(x),y) s1(plus2(x,y)) (19)
times2(0,y) 0 (20)
times2(s1(x),y) plus2(times2(x,y),y) (21)
map2(f,nil) nil (22)
map2(f,cons2(x,xs)) cons2(app(f,x),map2(f,xs)) (23)
inc map1(plus1(s1(0))) (24)
double map1(times1(s1(s1(0)))) (25)
app(plus,y1) plus1(y1) (9)
app(plus1(x0),y1) plus2(x0,y1) (10)
app(s,y1) s1(y1) (11)
app(times,y1) times1(y1) (12)
app(times1(x0),y1) times2(x0,y1) (13)
app(map,y1) map1(y1) (14)
app(map1(x0),y1) map2(x0,y1) (15)
app(cons,y1) cons1(y1) (16)
app(cons1(x0),y1) cons2(x0,y1) (17)

1.1 Rule Removal

Using the
prec(plus2) = 1 stat(plus2) = mul
prec(0) = 2 stat(0) = mul
prec(s1) = 0 stat(s1) = mul
prec(times2) = 3 stat(times2) = mul
prec(map2) = 5 stat(map2) = lex
prec(nil) = 6 stat(nil) = mul
prec(cons2) = 4 stat(cons2) = mul
prec(app) = 5 stat(app) = lex
prec(inc) = 7 stat(inc) = mul
prec(map1) = 5 stat(map1) = lex
prec(plus1) = 5 stat(plus1) = lex
prec(double) = 8 stat(double) = mul
prec(plus) = 9 stat(plus) = mul
prec(s) = 10 stat(s) = mul
prec(times) = 11 stat(times) = mul
prec(map) = 12 stat(map) = mul
prec(cons) = 0 stat(cons) = mul
prec(cons1) = 0 stat(cons1) = lex

π(plus2) = [1,2]
π(0) = []
π(s1) = [1]
π(times2) = [1,2]
π(map2) = [2,1]
π(nil) = []
π(cons2) = [1,2]
π(app) = [2,1]
π(inc) = []
π(map1) = [1]
π(plus1) = [1]
π(double) = []
π(times1) = 1
π(plus) = []
π(s) = []
π(times) = []
π(map) = []
π(cons) = []
π(cons1) = [1]

all of the following rules can be deleted.
plus2(0,y) y (18)
plus2(s1(x),y) s1(plus2(x,y)) (19)
times2(0,y) 0 (20)
times2(s1(x),y) plus2(times2(x,y),y) (21)
map2(f,nil) nil (22)
map2(f,cons2(x,xs)) cons2(app(f,x),map2(f,xs)) (23)
inc map1(plus1(s1(0))) (24)
double map1(times1(s1(s1(0)))) (25)
app(plus,y1) plus1(y1) (9)
app(plus1(x0),y1) plus2(x0,y1) (10)
app(s,y1) s1(y1) (11)
app(times,y1) times1(y1) (12)
app(times1(x0),y1) times2(x0,y1) (13)
app(map,y1) map1(y1) (14)
app(map1(x0),y1) map2(x0,y1) (15)
app(cons,y1) cons1(y1) (16)
app(cons1(x0),y1) cons2(x0,y1) (17)

1.1.1 R is empty

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