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Question 8203: Closed-Interval Intersection Including Touching Endpoints

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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R0015-08203 · q-20261012-advance-20261017-r04-order-relation-0028

Original question and givens

Use the usual total order on R, restricted to exact rational inputs whose original denominators are positive. Output reduced fractions with positive denominators, retaining /1; do not extrapolate to arbitrary partial orders or complex numbers. Intervals are [0/1, 0/1] and [0/1, 0/1]. Give (first endpoints, second endpoints, maximum lower bound, minimum upper bound, nonempty?, intersection endpoints or empty-set).

  • G001 — Use the usual total order on R, restricted to exact rational inputs whose original denominators are positive. Output reduced fractions with positive denominators, retaining /1; do not extrapolate to arbitrary partial orders or complex numbers. Intervals are [0/1, 0/1] and [0/1, 0/1]. Give (first endpoints, second endpoints, maximum lower bound, minimum upper bound, nonempty?, intersection endpoints or empty-set).

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

usual total order on R;all original denominators positive

After

closed endpoints included;negative scaling reverses;zero collapses

Conditions: none

These exact rationals use the usual real total order,not complex numbers or an arbitrary partial order.Original denominators must be positive;normalizing a negative input denominator does not waive that contract.

Step identifiers and dependencies

Rule: real_rational_order_scope · Uses: G001

S002 · calculation

Before

lower bounds left cross := mul(0, 1)

After

lower bounds left cross = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · calculation

Before

lower bounds right cross := mul(0, 1)

After

lower bounds right cross = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

lower bounds cross residual := sub(0, 0)

After

lower bounds cross residual = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · implies

Before

lower bounds:fractions=[0/1, 0/1]

After

cross residual=0;comparison==

Conditions: none

Reduced denominators are positive,so the cross-difference sign determines order.Retain equality and use original indices separately to break equal-value sorting ties.

Step identifiers and dependencies

Rule: rational_positive_denominator_comparison · Uses: G001, S004

S006 · calculation

Before

upper bounds left cross := mul(0, 1)

After

upper bounds left cross = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

upper bounds right cross := mul(0, 1)

After

upper bounds right cross = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · calculation

Before

upper bounds cross residual := sub(0, 0)

After

upper bounds cross residual = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · implies

Before

upper bounds:fractions=[0/1, 0/1]

After

cross residual=0;comparison==

Conditions: none

Reduced denominators are positive,so the cross-difference sign determines order.Retain equality and use original indices separately to break equal-value sorting ties.

Step identifiers and dependencies

Rule: rational_positive_denominator_comparison · Uses: G001, S008

S010 · calculation

Before

intersection inner bounds left cross := mul(0, 1)

After

intersection inner bounds left cross = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S009

S011 · calculation

Before

intersection inner bounds right cross := mul(0, 1)

After

intersection inner bounds right cross = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S010

S012 · calculation

Before

intersection inner bounds cross residual := sub(0, 0)

After

intersection inner bounds cross residual = 0

Conditions: none

Substitute the source data exactly in the stated operand order;division requires a nonzero denominator.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S011

S013 · implies

Before

intersection inner bounds:fractions=[0/1, 0/1]

After

cross residual=0;comparison==

Conditions: none

Reduced denominators are positive,so the cross-difference sign determines order.Retain equality and use original indices separately to break equal-value sorting ties.

Step identifiers and dependencies

Rule: rational_positive_denominator_comparison · Uses: G001, S012

S014 · implies

Before

intervals=[[0/1, 0/1], [0/1, 0/1]]

After

max lower=0/1;min upper=0/1;nonempty=Yes

Conditions: none

Satisfying both lower bounds means using their maximum;both upper bounds means their minimum.Equal inner bounds still include that single point.

Step identifiers and dependencies

Rule: closed_interval_intersection_guard · Uses: G001, S013

Reverse checks

  • S014 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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 — Recompute intersection inner bounds cross residual with exact rational arithmetic, not rounded decimals.
  • S011 · premise_and_result_audit — Recompute intersection inner bounds right cross with exact rational arithmetic, not rounded decimals.
  • S010 · premise_and_result_audit — Recompute intersection inner bounds left cross 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 — Recompute upper bounds cross residual with exact rational arithmetic, not rounded decimals.
  • S007 · premise_and_result_audit — Recompute upper bounds right cross with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute upper bounds left cross 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 lower bounds cross residual with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute lower bounds right cross with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Recompute lower bounds left cross 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, 0/1], [0/1, 0/1], 0/1, 0/1, Yes, [0/1, 0/1])

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: 4569171c2f2cff25c75be40621f75445d30a0cc51da3bc328324afd0c9cd38bf
  • candidate record SHA-256: d8157505c06d55cf4e601a4beceb3495c6310767a44f44ede98e8d1ed54f5a83
  • semantic review receipt SHA-256: 6ecad9d909199221a07e923f87425e80b3bdec3eed46fe5910d04fca694cae18
  • question-first witness SHA-256: e8f00458977a09493b5f9f05ab9e6feec72debaf4c7d1c609d1fc95900a35a1b
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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