Certification Problem

Input (TPDB TRS_Standard/AotoYamada_05/Ex5TermProof)

The rewrite relation of the following TRS is considered.

app(app(add,0),y) y (1)
app(app(add,app(s,x)),y) app(s,app(app(add,x),y)) (2)
app(app(mult,0),y) 0 (3)
app(app(mult,app(s,x)),y) app(app(add,app(app(mult,x),y)),y) (4)
app(app(app(rec,f),x),0) x (5)
app(app(app(rec,f),x),app(s,y)) app(app(f,app(s,y)),app(app(app(rec,f),x),y)) (6)
fact app(app(rec,mult),app(s,0)) (7)

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.

add is mapped to add, add1(x1), add2(x1, x2)
0 is mapped to 0
s is mapped to s, s1(x1)
mult is mapped to mult, mult1(x1), mult2(x1, x2)
rec is mapped to rec, rec1(x1), rec2(x1, x2), rec3(x1, x2, x3)
fact is mapped to fact


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
add2(0,y) y (16)
add2(s1(x),y) s1(add2(x,y)) (17)
mult2(0,y) 0 (18)
mult2(s1(x),y) add2(mult2(x,y),y) (19)
rec3(f,x,0) x (20)
rec3(f,x,s1(y)) app(app(f,s1(y)),rec3(f,x,y)) (21)
fact rec2(mult,s1(0)) (22)
app(add,y1) add1(y1) (8)
app(add1(x0),y1) add2(x0,y1) (9)
app(s,y1) s1(y1) (10)
app(mult,y1) mult1(y1) (11)
app(mult1(x0),y1) mult2(x0,y1) (12)
app(rec,y1) rec1(y1) (13)
app(rec1(x0),y1) rec2(x0,y1) (14)
app(rec2(x0,x1),y1) rec3(x0,x1,y1) (15)

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.
add2#(s1(x),y) add2#(x,y) (23)
mult2#(s1(x),y) add2#(mult2(x,y),y) (24)
mult2#(s1(x),y) mult2#(x,y) (25)
rec3#(f,x,s1(y)) app#(app(f,s1(y)),rec3(f,x,y)) (26)
rec3#(f,x,s1(y)) app#(f,s1(y)) (27)
rec3#(f,x,s1(y)) rec3#(f,x,y) (28)
app#(add1(x0),y1) add2#(x0,y1) (29)
app#(mult1(x0),y1) mult2#(x0,y1) (30)
app#(rec2(x0,x1),y1) rec3#(x0,x1,y1) (31)

1.1.1.1 Dependency Graph Processor

The dependency pairs are split into 3 components.