Certification Problem

Input (TPDB TRS_Standard/AProVE_07/wiehe06)

The rewrite relation of the following TRS is considered.

Property / Task

Answer / Result

Proof (by ttt2 @ termCOMP 2023)

1 Dependency Pair Transformation

1.1 Dependency Graph Processor

The dependency pairs are split into 3 components.

• The 1^st component contains the pair

  times#(x,plus(y,1))

  →

  times#(x,plus(y,times(1,0)))

  (17)

  1.1.1 Reduction Pair Processor with Usable Rules

  Using the linear polynomial interpretation over the naturals

  [s(x1)]	=	0 · x1 + 0
  [id(x1)]	=	0 · x1 + 1
  [plus(x1, x2)]	=	0 · x1 + 2 · x2 + 0
  [0]	=	0
  [gt(x1, x2)]	=	2 · x1 + 2 · x2 + 6
  [true]	=	0
  [1]	=	1
  [not(x1)]	=	0 · x1 + 1
  [times#(x1, x2)]	=	0 · x1 + 4 · x2 + 3
  [false]	=	6
  [zero]	=	3
  [if(x1, x2, x3)]	=	1 · x1 + 0 · x2 + 4 · x3 + 4
  [times(x1, x2)]	=	0 · x1 + 0 · x2 + 0

  together with the usable rules

  times(x,0)	→	0	(3)
  plus(s(x),s(y))	→	s(s(plus(if(gt(x,y),x,y),if(not(gt(x,y)),id(x),id(y)))))	(4)
  plus(s(x),x)	→	plus(if(gt(x,x),id(x),id(x)),s(x))	(5)
  plus(zero,y)	→	y	(6)
  plus(id(x),s(y))	→	s(plus(x,if(gt(s(y),y),y,s(y))))	(7)

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

  times#(x,plus(y,1))

  →

  times#(x,plus(y,times(1,0)))

  (17)

  could be deleted.

  1.1.1.1 P is empty

  There are no pairs anymore.

• The 2^nd component contains the pair

  plus#(id(x),s(y))	→	plus#(x,if(gt(s(y),y),y,s(y)))	(32)
  plus#(s(x),x)	→	plus#(if(gt(x,x),id(x),id(x)),s(x))	(29)
  plus#(s(x),s(y))	→	plus#(if(gt(x,y),x,y),if(not(gt(x,y)),id(x),id(y)))	(25)

  1.1.2 Reduction Pair Processor with Usable Rules

  Using the linear polynomial interpretation over the arctic semiring over the integers

  [s(x1)]	=	4 · x1 + 6
  [id(x1)]	=	0 · x1 + 4
  [gt(x1, x2)]	=	-∞ · x1 + -∞ · x2 + 0
  [true]	=	0
  [not(x1)]	=	0 · x1 + 4
  [false]	=	0
  [zero]	=	5
  [plus#(x1, x2)]	=	0 · x1 + 0 · x2 + 0
  [if(x1, x2, x3)]	=	0 · x1 + 0 · x2 + 0 · x3 + 1

  together with the usable rules

  gt(s(x),zero)	→	true	(12)
  gt(s(x),s(y))	→	gt(x,y)	(14)
  gt(zero,y)	→	false	(13)
  if(true,x,y)	→	x	(9)
  if(false,x,y)	→	y	(10)
  id(x)	→	x	(8)
  not(x)	→	if(x,false,true)	(11)

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

  plus#(s(x),s(y))

  →

  plus#(if(gt(x,y),x,y),if(not(gt(x,y)),id(x),id(y)))

  (25)

  could be deleted.

  1.1.2.1 Reduction Pair Processor with Usable Rules

  Using the

  prec(plus#)	=	0		stat(plus#)	=	lex
  prec(false)	=	0		stat(false)	=	lex
  prec(true)	=	0		stat(true)	=	lex
  prec(zero)	=	0		stat(zero)	=	lex
  prec(id)	=	0		stat(id)	=	lex
  prec(if)	=	0		stat(if)	=	lex
  prec(gt)	=	0		stat(gt)	=	lex
  prec(s)	=	5		stat(s)	=	lex

  π(plus#)	=	[1]
  π(false)	=	[]
  π(true)	=	[]
  π(zero)	=	[]
  π(id)	=	1
  π(if)	=	[2,3]
  π(gt)	=	1
  π(s)	=	[1]

  together with the usable rules

  if(true,x,y)	→	x	(9)
  if(false,x,y)	→	y	(10)
  id(x)	→	x	(8)

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

  plus#(s(x),x)

  →

  plus#(if(gt(x,x),id(x),id(x)),s(x))

  (29)

  could be deleted.

  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.

  plus#(id(x),s(y))	→	plus#(x,if(gt(s(y),y),y,s(y)))	(32)
  1	>	1

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

• The 3^rd component contains the pair

  gt#(s(x),s(y))

  →

  gt#(x,y)

  (34)

  1.1.3 Size-Change Termination

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

  gt#(s(x),s(y))	→	gt#(x,y)	(34)
  2	>	2
  1	>	1

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