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Question 20515: Finite Nonempty Real Sets Attain Both Their Bounds

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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R0040-20515 · q-20261014-advance-20261107-r02-supremum-and-infimum-0015

Original question and givens

The ordered rational values=[15/16, -16/17, 31/18] denote a complete nonempty finite real set. Duplicate listed values do not change its bounds; retain supplied order in the output. Empty, unbounded and extended-real sets are outside this slice. Give (values, supremum, infimum, supremum_attained, infimum_attained, certificate).

  • G001 — The ordered rational values=[15/16, -16/17, 31/18] denote a complete nonempty finite real set. Duplicate listed values do not change its bounds; retain supplied order in the output. Empty, unbounded and extended-real sets are outside this slice. Give (values, supremum, infimum, supremum_attained, infimum_attained, 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=supinf-finite-extrema;original snapshot and mathematics retained

After

explicit ordered source output fields=[values, supremum, infimum, supremum_attained, infimum_attained, certificate]

Conditions: none

Keep the historical interface marker in the original snapshot while listing source fields here without JavaScript or external lookup.Labels are not mathematical evidence,and No retains its source claim scope.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

ORIGINAL complete ordered nonempty finite real-value list=[15/16, -16/17, 31/18]

After

initialize upper/lower extremum candidates at ORIGINAL first value;duplicates retained and do not change set bounds

Conditions: none

This is the supplied complete finite set list,not a sample of an unspecified set.Duplicates do not alter bounds but remain in original output order;do not sort the data first.

Step identifiers and dependencies

Rule: supinf_complete_nonempty_finite_set_not_samples_or_sorting · Uses: G001, S001

S003 · calculation

Before

supinf original value1 minus previous maximum := sub(-16/17, 15/16)

After

supinf original value1 minus previous maximum = -511/272

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,set positions,orientation,signs and applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

supinf original value1 minus previous minimum := sub(-16/17, 15/16)

After

supinf original value1 minus previous minimum = -511/272

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,set positions,orientation,signs and applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · implies

Before

ORIGINAL next index=1;value=-16/17;previous extremum values=[15/16, 15/16];differences=[-511/272, -511/272]

After

prefix maximum=15/16 attained at original index0;prefix minimum=-16/17 attained at original index1

Conditions: none

Compare every original value,preserving prefix maximum/minimum invariants and updating witnesses only for strict improvement.No original value is omitted.

Step identifiers and dependencies

Rule: supinf_every_value_extremum_prefix_invariant · Uses: G001, S004

S006 · calculation

Before

supinf original value2 minus previous maximum := sub(31/18, 15/16)

After

supinf original value2 minus previous maximum = 113/144

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,set positions,orientation,signs and applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

supinf original value2 minus previous minimum := sub(31/18, -16/17)

After

supinf original value2 minus previous minimum = 815/306

Conditions: none

Substitute original roles and established intermediates exactly,retaining indices,set positions,orientation,signs and applicability conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · implies

Before

ORIGINAL next index=2;value=31/18;previous extremum values=[15/16, -16/17];differences=[113/144, 815/306]

After

prefix maximum=31/18 attained at original index2;prefix minimum=-16/17 attained at original index1

Conditions: none

Compare every original value,preserving prefix maximum/minimum invariants and updating witnesses only for strict improvement.No original value is omitted.

Step identifiers and dependencies

Rule: supinf_every_value_extremum_prefix_invariant · Uses: G001, S007

S009 · implies

Before

ALL original values processed;actual maximum witness=[2, 31/18];actual minimum witness=[1, -16/17]

After

EVERY listed value between-16/17 and31/18;ANY upper bound must>=actual maximum in the set;ANY lower bound must<=actual minimum;sup=31/18,inf=-16/17,BOTH attained

Conditions: none

Because the maximum is itself in the set,no upper bound can be smaller;the minimum similarly bounds every lower bound above.This proves both bounding and leastness/greatestness.Attainment uses finiteness and nonemptiness and is not inferred for arbitrary bounded sets.

Step identifiers and dependencies

Rule: supinf_bounds_and_least_greatest_by_actual_attaining_points · Uses: G001, S008

Reverse checks

  • 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 supinf original value2 minus previous minimum with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute supinf original value2 minus previous maximum 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 supinf original value1 minus previous minimum with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute supinf original value1 minus previous maximum 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

([15/16, -16/17, 31/18], 31/18, -16/17, Yes, Yes, finite_nonempty_set_extrema)

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: ffd101b6ef09220a36e9b2df054549f91ce3f27e27a05a9ae853fe4345cc27ce
  • candidate record SHA-256: 7749f0abac4cecc970cc26a61089686c83ad7bca2baf7f6ffaf1bd7955205a55
  • semantic review receipt SHA-256: c6483ed1229af9183fe5c704a2627b1558ad9a31bfbb0d2ee2d5c1a1c299ab4d
  • question-first witness SHA-256: e81f9a560d630fcb23441146f008c4feca7aceab3ebe4de2cf1997c061375ef7
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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