Certification Problem

Input (TPDB TRS_Standard/AProVE_07/thiemann05)

The rewrite relation of the following TRS is considered.

Property / Task

Answer / Result

Proof (by AProVE @ termCOMP 2023)

1 Switch to Innermost Termination

The TRS is overlay and locally confluent:

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

1.1 Dependency Pair Transformation

1.1.1 Dependency Graph Processor

The dependency pairs are split into 2 components.

• The 1^st component contains the pair

  if2#(false,u,v)	→	less_leaves#(concat(left(u),right(u)),concat(left(v),right(v)))	(17)
  less_leaves#(u,v)	→	if1#(isLeaf(u),isLeaf(v),u,v)	(13)
  if1#(b,false,u,v)	→	if2#(b,u,v)	(16)

  1.1.1.1 Usable Rules Processor

  We restrict the rewrite rules to the following usable rules of the DP problem.

  isLeaf(leaf)	→	true	(1)
  isLeaf(cons(u,v))	→	false	(2)
  left(cons(u,v))	→	u	(3)
  right(cons(u,v))	→	v	(4)
  concat(leaf,y)	→	y	(5)
  concat(cons(u,v),y)	→	cons(u,concat(v,y))	(6)

  1.1.1.1.1 Innermost Lhss Removal Processor

  We restrict the innermost strategy to the following left hand sides.

  isLeaf(leaf)

  isLeaf(cons(x0,x1))

  left(cons(x0,x1))

  right(cons(x0,x1))

  concat(leaf,x0)

  concat(cons(x0,x1),x2)

  1.1.1.1.1.1 Narrowing Processor

  We consider all narrowings of the pair below position 2 to get the following set of pairs

  less_leaves#(y0,leaf)	→	if1#(isLeaf(y0),true,y0,leaf)	(24)
  less_leaves#(y0,cons(x0,x1))	→	if1#(isLeaf(y0),false,y0,cons(x0,x1))	(25)

  1.1.1.1.1.1.1 Dependency Graph Processor

  The dependency pairs are split into 1 component.

  • The 1^st component contains the pair

    less_leaves#(y0,cons(x0,x1))	→	if1#(isLeaf(y0),false,y0,cons(x0,x1))	(25)
    if1#(b,false,u,v)	→	if2#(b,u,v)	(16)
    if2#(false,u,v)	→	less_leaves#(concat(left(u),right(u)),concat(left(v),right(v)))	(17)

    1.1.1.1.1.1.1.1 Narrowing Processor

    We consider all narrowings of the pair below position 2 to get the following set of pairs

    if2#(false,y0,cons(x0,x1))	→	less_leaves#(concat(left(y0),right(y0)),concat(x0,right(cons(x0,x1))))	(26)
    if2#(false,y0,cons(x0,x1))	→	less_leaves#(concat(left(y0),right(y0)),concat(left(cons(x0,x1)),x1))	(27)

    1.1.1.1.1.1.1.1.1 Rewriting Processor

    We rewrite the right hand side of the pair resulting in

    →

    1.1.1.1.1.1.1.1.1.1 Rewriting Processor

    We rewrite the right hand side of the pair resulting in

    →

    1.1.1.1.1.1.1.1.1.1.1 Reduction Pair Processor with Usable Rules

    Using the Knuth Bendix order with w0 = 1 and the following precedence and weight functions

    prec(cons)	=	0		weight(cons)	=	2
    prec(concat)	=	1		weight(concat)	=	1
    prec(leaf)	=	2		weight(leaf)	=	1

    in combination with the following argument filter

    π(less_leaves#)	=	2
    π(cons)	=	[1,2]
    π(if1#)	=	4
    π(if2#)	=	3
    π(concat)	=	[1,2]
    π(leaf)	=	[]

    together with the usable rules

    concat(leaf,y)	→	y	(5)
    concat(cons(u,v),y)	→	cons(u,concat(v,y))	(6)

    (w.r.t. the implicit argument filter of the reduction pair), the pair

    if2#(false,y0,cons(x0,x1))

    →

    less_leaves#(concat(left(y0),right(y0)),concat(x0,x1))

    (28)

    could be deleted.

    1.1.1.1.1.1.1.1.1.1.1.1 Dependency Graph Processor

    The dependency pairs are split into 0 components.

• The 2^nd component contains the pair

  concat#(cons(u,v),y)

  →

  concat#(v,y)

  (12)

  1.1.1.2 Usable Rules Processor

  We restrict the rewrite rules to the following usable rules of the DP problem.

  There are no rules.

  1.1.1.2.1 Innermost Lhss Removal Processor

  We restrict the innermost strategy to the following left hand sides.

  There are no lhss.

  1.1.1.2.1.1 Size-Change Termination

  Using size-change termination in combination with the subterm criterion one obtains the following initial size-change graphs.

  concat#(cons(u,v),y)	→	concat#(v,y)	(12)
  1	>	1
  2	≥	2

  As there is no critical graph in the transitive closure, there are no infinite chains.