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Question 1523: Every Fixed Point of the Given Finite Self-Map

On this page
  1. Original question and givens
  2. Definition and scope
  3. Step-by-step derivation
  4. Reverse checks
  5. Result
  6. This question review and source binding

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← Question derivation index · Original question batch

R0002-01523 · q-20261013-advance-20261020-r01-discrete-dynamical-system-0073

Original question and givens

Use the complete finite self-map on Fin(9)={0,…,8} given by T(x)=(a*x+b) mod 9, a=18, b=45. Choose the least nonnegative residue, including for negative a*x+b. Time is discrete, indexed from 0; a finite orbit is not a general stability result. Give (modulus, a, b, every x with T(x)=x in increasing order).

  • G001 — Use the complete finite self-map on Fin(9)={0,…,8} given by T(x)=(a*x+b) mod 9, a=18, b=45. Choose the least nonnegative residue, including for negative a*x+b. Time is discrete, indexed from 0; a finite orbit is not a general stability result. Give (modulus, a, b, every x with T(x)=x in increasing order).

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

Step-by-step derivation

S001 · implies

Before

X={0 through 8}; T(x)=(18x+(45)) mod 9

After

remainder representative always lies in X

Conditions: none

Fix the full finite state carrier and the same update rule;negative integers also use the standard remainder from0 through n−1.

Step identifiers and dependencies

Rule: finite_total_map · Uses: G001

S002 · calculation

Before

candidate0: a·x := mul(18, 0)

After

candidate0: a·x = 0

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · calculation

Before

candidate0: a·x+b := sum(0, 45)

After

candidate0: a·x+b = 45

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · implies

Before

reduce 45 modulo 9

After

45=5·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S003

S005 · implies

Before

T(0)=0

After

fixed-point condition T(x)=x: Yes

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S004

S006 · calculation

Before

candidate1: a·x := mul(18, 1)

After

candidate1: a·x = 18

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

candidate1: a·x+b := sum(18, 45)

After

candidate1: a·x+b = 63

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · implies

Before

reduce 63 modulo 9

After

63=7·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S007

S009 · implies

Before

T(1)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S008

S010 · calculation

Before

candidate2: a·x := mul(18, 2)

After

candidate2: a·x = 36

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S009

S011 · calculation

Before

candidate2: a·x+b := sum(36, 45)

After

candidate2: a·x+b = 81

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S010

S012 · implies

Before

reduce 81 modulo 9

After

81=9·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S011

S013 · implies

Before

T(2)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S012

S014 · calculation

Before

candidate3: a·x := mul(18, 3)

After

candidate3: a·x = 54

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S013

S015 · calculation

Before

candidate3: a·x+b := sum(54, 45)

After

candidate3: a·x+b = 99

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S014

S016 · implies

Before

reduce 99 modulo 9

After

99=11·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S015

S017 · implies

Before

T(3)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S016

S018 · calculation

Before

candidate4: a·x := mul(18, 4)

After

candidate4: a·x = 72

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S017

S019 · calculation

Before

candidate4: a·x+b := sum(72, 45)

After

candidate4: a·x+b = 117

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S018

S020 · implies

Before

reduce 117 modulo 9

After

117=13·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S019

S021 · implies

Before

T(4)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S020

S022 · calculation

Before

candidate5: a·x := mul(18, 5)

After

candidate5: a·x = 90

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S021

S023 · calculation

Before

candidate5: a·x+b := sum(90, 45)

After

candidate5: a·x+b = 135

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S022

S024 · implies

Before

reduce 135 modulo 9

After

135=15·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S023

S025 · implies

Before

T(5)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S024

S026 · calculation

Before

candidate6: a·x := mul(18, 6)

After

candidate6: a·x = 108

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S025

S027 · calculation

Before

candidate6: a·x+b := sum(108, 45)

After

candidate6: a·x+b = 153

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S026

S028 · implies

Before

reduce 153 modulo 9

After

153=17·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S027

S029 · implies

Before

T(6)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S028

S030 · calculation

Before

candidate7: a·x := mul(18, 7)

After

candidate7: a·x = 126

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S029

S031 · calculation

Before

candidate7: a·x+b := sum(126, 45)

After

candidate7: a·x+b = 171

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S030

S032 · implies

Before

reduce 171 modulo 9

After

171=19·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S031

S033 · implies

Before

T(7)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S032

S034 · calculation

Before

candidate8: a·x := mul(18, 8)

After

candidate8: a·x = 144

Conditions: none

Multiply the original coefficient by the current state;do not clip negative values to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S033

S035 · calculation

Before

candidate8: a·x+b := sum(144, 45)

After

candidate8: a·x+b = 189

Conditions: none

Add the same offset before reducing modulo n.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S034

S036 · implies

Before

reduce 189 modulo 9

After

189=21·9+0

Conditions: none

The integer identity together with0≤remainder<n determines the next state.

Step identifiers and dependencies

Rule: euclidean_remainder · Uses: G001, S035

S037 · implies

Before

T(8)=0

After

fixed-point condition T(x)=x: No

Conditions: none

A fixed point must remain the same state after updating;merely remaining in the carrier is insufficient.

Step identifiers and dependencies

Rule: fixed_point_equality · Uses: G001, S036

S038 · implies

Before

all 9 carrier elements audited

After

complete fixed set=[0]

Conditions: none

The full finite carrier was exhausted,so no fixed point is omitted;an empty list means this T has none.

Step identifiers and dependencies

Rule: exhaustive_fixed_inventory · Uses: G001, S037

Reverse checks

  • S038 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S037 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S036 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S035 · premise_and_result_audit — Recompute candidate8: a·x+b with exact rational arithmetic, not rounded decimals.
  • S034 · premise_and_result_audit — Recompute candidate8: a·x with exact rational arithmetic, not rounded decimals.
  • S033 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S032 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S031 · premise_and_result_audit — Recompute candidate7: a·x+b with exact rational arithmetic, not rounded decimals.
  • S030 · premise_and_result_audit — Recompute candidate7: a·x with exact rational arithmetic, not rounded decimals.
  • S029 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S028 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S027 · premise_and_result_audit — Recompute candidate6: a·x+b with exact rational arithmetic, not rounded decimals.
  • S026 · premise_and_result_audit — Recompute candidate6: a·x with exact rational arithmetic, not rounded decimals.
  • S025 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S024 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S023 · premise_and_result_audit — Recompute candidate5: a·x+b with exact rational arithmetic, not rounded decimals.
  • S022 · premise_and_result_audit — Recompute candidate5: a·x with exact rational arithmetic, not rounded decimals.
  • S021 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S020 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S019 · premise_and_result_audit — Recompute candidate4: a·x+b with exact rational arithmetic, not rounded decimals.
  • S018 · premise_and_result_audit — Recompute candidate4: a·x with exact rational arithmetic, not rounded decimals.
  • S017 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S016 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S015 · premise_and_result_audit — Recompute candidate3: a·x+b with exact rational arithmetic, not rounded decimals.
  • S014 · premise_and_result_audit — Recompute candidate3: a·x with exact rational arithmetic, not rounded decimals.
  • S013 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S012 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S011 · premise_and_result_audit — Recompute candidate2: a·x+b with exact rational arithmetic, not rounded decimals.
  • S010 · premise_and_result_audit — Recompute candidate2: a·x with exact rational arithmetic, not rounded decimals.
  • S009 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S008 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S007 · premise_and_result_audit — Recompute candidate1: a·x+b with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute candidate1: a·x with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S004 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S003 · premise_and_result_audit — Recompute candidate0: a·x+b with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Recompute candidate0: a·x with exact rational arithmetic, not rounded decimals.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(9, 18, 45, [0])

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.

Source hashes and review receipts
  • input commit: 0f7be61e2c22317a4075561dc822c87d881a50db
  • original question SHA-256: 52f227478e4f6b216816551d136c93562a4116933f2c85debd732b06f7af17f6
  • candidate record SHA-256: fe31787ee599f8d5cde3dcdf4ded869604ead33052d7d92b68588c89982d7236
  • semantic review receipt SHA-256: 340d74dcc6e37df6249594a0b79a9ee2af804337b7847478b3c1342af9722861
  • question-first witness SHA-256: 9a06233d190d31a16f13fb03b6c3ceba4cbb748fff6c997941f66ab1888dcca8
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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