Certification Problem

Input (TPDB TRS_Standard/AotoYamada_05/010)

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(app(curry,g),x),y) app(app(g,x),y) (5)
app(app(map,f),nil) nil (6)
app(app(map,f),app(app(cons,x),xs)) app(app(cons,app(f,x)),app(app(map,f),xs)) (7)
inc app(map,app(app(curry,plus),app(s,0))) (8)
double app(map,app(app(curry,times),app(s,app(s,0)))) (9)

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)
curry is mapped to curry, curry1(x1), curry2(x1, x2), curry3(x1, x2, x3)
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 (22)
plus2(s1(x),y) s1(plus2(x,y)) (23)
times2(0,y) 0 (24)
times2(s1(x),y) plus2(times2(x,y),y) (25)
curry3(g,x,y) app(app(g,x),y) (26)
map2(f,nil) nil (27)
map2(f,cons2(x,xs)) cons2(app(f,x),map2(f,xs)) (28)
inc map1(curry2(plus,s1(0))) (29)
double map1(curry2(times,s1(s1(0)))) (30)
app(plus,y1) plus1(y1) (10)
app(plus1(x0),y1) plus2(x0,y1) (11)
app(s,y1) s1(y1) (12)
app(times,y1) times1(y1) (13)
app(times1(x0),y1) times2(x0,y1) (14)
app(curry,y1) curry1(y1) (15)
app(curry1(x0),y1) curry2(x0,y1) (16)
app(curry2(x0,x1),y1) curry3(x0,x1,y1) (17)
app(map,y1) map1(y1) (18)
app(map1(x0),y1) map2(x0,y1) (19)
app(cons,y1) cons1(y1) (20)
app(cons1(x0),y1) cons2(x0,y1) (21)

1.1 Switch to Innermost Termination

The TRS is overlay and locally confluent:

10

Hence, it suffices to show innermost termination in the following.

1.1.1 Dependency Pair Transformation

The following set of initial dependency pairs has been identified.
plus2#(s1(x),y) plus2#(x,y) (31)
times2#(s1(x),y) plus2#(times2(x,y),y) (32)
times2#(s1(x),y) times2#(x,y) (33)
curry3#(g,x,y) app#(app(g,x),y) (34)
curry3#(g,x,y) app#(g,x) (35)
map2#(f,cons2(x,xs)) app#(f,x) (36)
map2#(f,cons2(x,xs)) map2#(f,xs) (37)
app#(plus1(x0),y1) plus2#(x0,y1) (38)
app#(times1(x0),y1) times2#(x0,y1) (39)
app#(curry2(x0,x1),y1) curry3#(x0,x1,y1) (40)
app#(map1(x0),y1) map2#(x0,y1) (41)

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 3 components.