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Question 17503: A Strict Pointwise Tail Witness Can Depend on the Point

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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R0034-17503 · q-20261014-advance-20261103-r02-pointwise-convergence-of-functions-0028

Original question and givens

Use the same complete finite domain Fin(2)={0,…,1}, with aligned limit values=[2, 3], coefficients=[3, -4], positive shift=2, and f_n(x)=limit[x]+coefficients[x]/(n+shift) for every n≥0. Values and tail bounds are exact rationals. Pointwise witnesses may depend on both x and epsilon. A finite maximum of all pointwise witnesses gives a common witness only on this finite domain; it is not a general infinite-domain implication. A finite observed prefix alone is not a convergence certificate. Positive epsilon=1/12, point=0. Give (point,epsilon,N,error_at_N,strict_tail?,forall_n_ge_N), with error_at_N the absolute error bound.

  • G001 — Use the same complete finite domain Fin(2)={0,…,1}, with aligned limit values=[2, 3], coefficients=[3, -4], positive shift=2, and f_n(x)=limit[x]+coefficients[x]/(n+shift) for every n≥0. Values and tail bounds are exact rationals. Pointwise witnesses may depend on both x and epsilon. A finite maximum of all pointwise witnesses gives a common witness only on this finite domain; it is not a general infinite-domain implication. A finite observed prefix alone is not a convergence certificate. Positive epsilon=1/12, point=0. Give (point,epsilon,N,error_at_N,strict_tail?,forall_n_ge_N), with error_at_N the absolute error bound.

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

same COMPLETE finite domain Fin(2);original aligned limits=[2, 3];signed coefficients=[3, -4];positive shift=2

After

declared for EVERY n>=0:f_n(x)=limit[x]+coefficient[x]/(n+shift);signed error=f_n(x)-limit[x]=coefficient[x]/(n+shift)

Conditions: none

The complete common finite domain and all-n formula are declared premises,not extrapolated from samples.Function values and errors are not probabilities;they may be signed or exceed1.Do not clip or shift indices.

Step identifiers and dependencies

Rule: pointwise_explicit_common_domain_all_n_tail_not_probability · Uses: G001

S002 · calculation

Before

selected pointwise witness absolute coefficient cross product := mul(3, 12)

After

selected pointwise witness absolute coefficient cross product = 36

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · calculation

Before

selected pointwise witness strict reciprocal threshold := div(36, 1)

After

selected pointwise witness strict reciprocal threshold = 36

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

selected pointwise witness raw strict integer cutoff := sum(36, -2, 1)

After

selected pointwise witness raw strict integer cutoff = 35

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · implies

Before

selected pointwise witness:point=0;SIGNED coefficient=3;absolute coefficient=3;positive epsilon=1/12;shift=2

After

threshold=36;floor=36;least nonnegative strict cutoff N=35

Conditions: none

The strict inequality is N+s>|c|b/a,so take its floor plus1 minus shift and clamp only at0.Equality is insufficient and a zero coefficient permits N=0.No probability≤1 guard belongs here.

Step identifiers and dependencies

Rule: pointwise_least_strict_cutoff_floor_not_probability_guard · Uses: G001, S004

S006 · calculation

Before

selected pointwise witness cutoff denominator := sum(35, 2)

After

selected pointwise witness cutoff denominator = 37

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

selected pointwise witness absolute error at cutoff := div(3, 37)

After

selected pointwise witness absolute error at cutoff = 3/37

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · calculation

Before

selected pointwise witness previous denominator := sum(34, 2)

After

selected pointwise witness previous denominator = 36

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · calculation

Before

selected pointwise witness previous absolute error := div(3, 36)

After

selected pointwise witness previous absolute error = 1/12

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S008

S010 · implies

Before

selected pointwise witness:current N=35;current error=3/37;previous error=1/12;epsilon=1/12

After

current strict bound holds;previous fails;all smaller indices fail by monotonicity

Conditions: none

The preceding error is still≥epsilon.As denominators increase with n,every smaller nonnegative index also fails the strict bound.

Step identifiers and dependencies

Rule: pointwise_minimality_previous_index_strict_threshold · Uses: G001, S009

S011 · implies

Before

selected pointwise witness:declared exact tail;positive denominators increase for all n>=N=35

After

for EVERY later n,absolute error<=bound=3/37<epsilon=1/12

Conditions: none

The same declared formula bounds every later denominator,which supplies an all-tail bound rather than a conclusion about an unknown sequence from one successful value.

Step identifiers and dependencies

Rule: pointwise_all_later_tail_not_single_numeric_sample · Uses: G001, S010

Reverse checks

  • S011 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S010 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S009 · premise_and_result_audit — Recompute selected pointwise witness previous absolute error with exact rational arithmetic, not rounded decimals.
  • S008 · premise_and_result_audit — Recompute selected pointwise witness previous denominator with exact rational arithmetic, not rounded decimals.
  • S007 · premise_and_result_audit — Recompute selected pointwise witness absolute error at cutoff with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute selected pointwise witness cutoff denominator 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 — Recompute selected pointwise witness raw strict integer cutoff with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute selected pointwise witness strict reciprocal threshold with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Recompute selected pointwise witness absolute coefficient cross product 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

(0, 1/12, 35, 3/37, Yes, forall_n_ge_N)

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: 95fc00527092b041f50d79eb04f2ff339c3df83ea528453c6c79b700db083c72
  • candidate record SHA-256: 61b6436e442400414056f00335987c0221d7ca136e95a76f8626496dedab7546
  • semantic review receipt SHA-256: f73d099ebe3ff1c69a5d96f08c75b11b9e5b05120af40cf3ef388fce3b5c5336
  • question-first witness SHA-256: 22675ffb6209b4fea076032b29b96e3dc19aad4244c54493f5f65f5e5d875699
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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