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Question 20421: A Subsequence Term Uses the Source at Its Increasing Selected Index

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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R0039-20421 · q-20261014-advance-20261107-r07-subsequence-0046

Original question and givens

Use the entire arithmetic source a_n=21+(7)n for n≥0 and index map k(j)=0+1j, with nonnegative start and positive index step. Evaluate j=22. Give (j, source_index, subsequence_term, certificate).

  • G001 — Use the entire arithmetic source a_n=21+(7)n for n≥0 and index map k(j)=0+1j, with nonnegative start and positive index step. Evaluate j=22. Give (j, source_index, subsequence_term, certificate).

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

source operation=subseq-arithmetic-term;original snapshot and mathematics retained

After

explicit ordered source output fields=[j, source_index, subsequence_term, certificate]

Conditions: none

Retain the historical interface marker in the original snapshot while listing ordered source fields here,without JavaScript or external lookup.Field labels are not additional mathematical evidence,and No retains the source claim scope.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

original subsequence index k:ORIGINAL nonnegative start=0;positive integer step=1;F(q)=start+step*q for EVERY natural q>=0

After

F(q)>=start>=0 and for ANY q<r,F(r)-F(q)=(1)*(r-q)>0;strictly increasing on ALL naturals,not just the evaluated prefix

Conditions: none

A positive integer step preserves the order of every pair of natural indices,not merely injectivity or an arbitrary reordering.This universal mathematical law is not truncated by an evaluated-output safety range and says nothing about monotonicity of source values.

Step identifiers and dependencies

Rule: subseq_affine_all_natural_index_order_not_value_monotonicity · Uses: G001, S001

S003 · calculation

Before

subsequence selected index step times j := mul(1, 22)

After

subsequence selected index step times j = 22

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,signs,denominators and the proof's applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

subsequence selected ORIGINAL source index := sum(0, 22)

After

subsequence selected ORIGINAL source index = 22

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,signs,denominators and the proof's applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · calculation

Before

subsequence ORIGINAL source step times selected index := mul(7, 22)

After

subsequence ORIGINAL source step times selected index = 154

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,signs,denominators and the proof's applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S004

S006 · calculation

Before

subsequence value of ORIGINAL source at selected index := sum(21, 154)

After

subsequence value of ORIGINAL source at selected index = 175

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,signs,denominators and the proof's applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · implies

Before

ORIGINAL arithmetic source a_n=21+(7)n;increasing selected index k(22)=22

After

a_at_selected_index=175;ORIGINAL index order retained even if source step=7 is negative or0;no value sorting

Conditions: none

Compute the selected index and substitute it into the original source formula.Source steps may be negative or0:a subsequence preserves index order,not increasing values.Sorting the resulting values would not produce this stated subsequence.

Step identifiers and dependencies

Rule: subseq_selected_source_order_not_reordered_values · Uses: G001, S006

Reverse checks

  • S007 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S006 · premise_and_result_audit — Recompute subsequence value of ORIGINAL source at selected index with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Recompute subsequence ORIGINAL source step times selected index with exact rational arithmetic, not rounded decimals.
  • S004 · premise_and_result_audit — Recompute subsequence selected ORIGINAL source index with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute subsequence selected index step times j with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(22, 22, 175, a_of_k_j_preserves_original_order)

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: 25b7918c2a7f5659f3c74e0a9fa5ee189e41fa105654b0fe73e13e87747b3099
  • candidate record SHA-256: cb036bd1dc81696bc1374156b0d037469d320b1557159b5909333583a637b533
  • semantic review receipt SHA-256: 6e11e35fafe32f16900ce9b522d01acb7b2ee6b463ab179392076cfbe1af8034
  • question-first witness SHA-256: cc0fa361fc25151729e70264340d2eae94f179f6f2a2edfe80ba5704fbbd0682
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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