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Question 10507: A Strict Open Ball in a Complete Finite Metric

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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R0020-10507 · q-20261013-advance-20261023-r04-metric-convergence-0007

Original question and givens

Use the complete qualified finite metric table=[[0, 7, 15, 24], [7, 0, 8, 17], [15, 8, 0, 9], [24, 17, 9, 0]] on Fin(4)={0,…,3}. Preserve the convergence quantifiers: for every positive epsilon there exists N such that every n≥N satisfies d(x_n,candidate)<epsilon. A finite recorded tail alone does not certify this infinite statement. center=2, positive epsilon=7/1. Give (carrier size,center,normalized epsilon,every label with distance from center strictly less than epsilon in increasing order). Use exact reduced rational outputs with positive denominators, omitting /1 for integers.

  • G001 — Use the complete qualified finite metric table=[[0, 7, 15, 24], [7, 0, 8, 17], [15, 8, 0, 9], [24, 17, 9, 0]] on Fin(4)={0,…,3}. Preserve the convergence quantifiers: for every positive epsilon there exists N such that every n≥N satisfies d(x_n,candidate)<epsilon. A finite recorded tail alone does not certify this infinite statement. center=2, positive epsilon=7/1. Give (carrier size,center,normalized epsilon,every label with distance from center strictly less than epsilon in increasing order). Use exact reduced rational outputs with positive denominators, omitting /1 for integers.

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

carrier Fin(4);complete distance table=[[0, 7, 15, 24], [7, 0, 8, 17], [15, 8, 0, 9], [24, 17, 9, 0]]

After

nonnegative typed entries=Yes;zero iff equal=Yes;symmetric=Yes;all triangle tests=Yes

Conditions: none

Qualify the whole metric table,not only queried cells.Labels are not distances:diagonal zero,positive separation,symmetry and every triangle condition are premises for later reasoning.

Step identifiers and dependencies

Rule: whole_qualified_finite_metric · Uses: G001

S002 · implies

Before

raw epsilon=[7, 1]

After

normalized positive epsilon=7

Conditions: none

The original denominator is nonzero and normalized epsilon must be positive.A negative original denominator may normalize legitimately;do not bypass the guard by totalized machine division.

Step identifiers and dependencies

Rule: metric_positive_epsilon_original_denominator · Uses: G001, S001

S003 · calculation

Before

ball state0 distance times epsilon denominator := mul(15, 1)

After

ball state0 distance times epsilon denominator = 15

Conditions: none

Compute exactly with this step's original roles and operands,without floating approximation or reordering source data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · implies

Before

ball state0:distance=15;epsilon=7;positive denominator=1

After

cross product=15;strictly below numerator=No

Conditions: none

Cross-multiply by the positive denominator and retain strict inequality.Equality with epsilon is outside the open ball.

Step identifiers and dependencies

Rule: strict_metric_distance_comparison · Uses: G001, S003

S005 · calculation

Before

ball state1 distance times epsilon denominator := mul(8, 1)

After

ball state1 distance times epsilon denominator = 8

Conditions: none

Compute exactly with this step's original roles and operands,without floating approximation or reordering source data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S004

S006 · implies

Before

ball state1:distance=8;epsilon=7;positive denominator=1

After

cross product=8;strictly below numerator=No

Conditions: none

Cross-multiply by the positive denominator and retain strict inequality.Equality with epsilon is outside the open ball.

Step identifiers and dependencies

Rule: strict_metric_distance_comparison · Uses: G001, S005

S007 · calculation

Before

ball state2 distance times epsilon denominator := mul(0, 1)

After

ball state2 distance times epsilon denominator = 0

Conditions: none

Compute exactly with this step's original roles and operands,without floating approximation or reordering source data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · implies

Before

ball state2:distance=0;epsilon=7;positive denominator=1

After

cross product=0;strictly below numerator=Yes

Conditions: none

Cross-multiply by the positive denominator and retain strict inequality.Equality with epsilon is outside the open ball.

Step identifiers and dependencies

Rule: strict_metric_distance_comparison · Uses: G001, S007

S009 · calculation

Before

ball state3 distance times epsilon denominator := mul(9, 1)

After

ball state3 distance times epsilon denominator = 9

Conditions: none

Compute exactly with this step's original roles and operands,without floating approximation or reordering source data.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S008

S010 · implies

Before

ball state3:distance=9;epsilon=7;positive denominator=1

After

cross product=9;strictly below numerator=No

Conditions: none

Cross-multiply by the positive denominator and retain strict inequality.Equality with epsilon is outside the open ball.

Step identifiers and dependencies

Rule: strict_metric_distance_comparison · Uses: G001, S009

S011 · implies

Before

center=2;strict radius=7;all carrier labels=[0, 1, 2, 3]

After

open ball=[2]

Conditions: none

Inspect the complete carrier,including the center and excluding the boundary.Do not infer the ball from label sizes or a drawing.

Step identifiers and dependencies

Rule: complete_strict_ball_inventory · 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 ball state3 distance times epsilon denominator with exact rational arithmetic, not rounded decimals.
  • 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 ball state2 distance times epsilon denominator with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S005 · premise_and_result_audit — Recompute ball state1 distance times epsilon denominator with exact rational arithmetic, not rounded decimals.
  • 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 ball state0 distance times epsilon denominator 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

(4, 2, 7, [2])

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: 478b56aad8c87e7a1faf1775a56733750283861a334e07ad45d48a3d3135e44b
  • candidate record SHA-256: be8ff1e87da3864b9afecb5d32b3b463e76f1e2afbde11eb219ef780e80a1415
  • semantic review receipt SHA-256: b4c47938fd38085d44967226cfa8337d61334455472e7307c60d3a488cef598f
  • question-first witness SHA-256: 3c23baa97a5933bc07b44f2257017ef4e845bf1429bd6f5381410681c43b97e4
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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