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Question 23572: Finite Intersections Separate an Exterior Point from the Whole Compact Subset

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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R0046-23572 · q-20261014-advance-20261112-r03-compact-subset-closed-in-hausdorff-0072

Original question and givens

Use complete finite labeled carrier=[a21, b21, c21], topology=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []] in its original supplied open-set order, and compact_subset K=[a21, b21]. Qualify the topology and every Hausdorff distinct-point pair. Finite K is compact; the general theorem still needs both ambient Hausdorffness and compactness. Exterior point x=c21 must lie outside K. Give (exterior_point, separation_rows, exterior_neighborhood, cover_union, covers_K, neighborhood_disjoint_from_K, neighborhood_open, certificate).

  • G001 — Use complete finite labeled carrier=[a21, b21, c21], topology=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []] in its original supplied open-set order, and compact_subset K=[a21, b21]. Qualify the topology and every Hausdorff distinct-point pair. Finite K is compact; the general theorem still needs both ambient Hausdorffness and compactness. Exterior point x=c21 must lie outside K. Give (exterior_point, separation_rows, exterior_neighborhood, cover_union, covers_K, neighborhood_disjoint_from_K, neighborhood_open, 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=compactclosed-neighborhood-subcover-certificate;original snapshot and mathematics retained

After

explicit ordered source output fields=[exterior_point, separation_rows, exterior_neighborhood, cover_union, covers_K, neighborhood_disjoint_from_K, neighborhood_open, certificate]

Conditions: none

Keep the source snapshot while listing ordered fields without JavaScript.Radius uses its original mode to select6 or11 fields without padding;distinguish nonclaims from actual negations.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

ORIGINAL carrier order=[a21, b21, c21];ORIGINAL open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []];point=a21;ALL given sets containing it have indices=[0, 1, 2, 3]

After

candidate N(a21)=intersection of ALL those sets=[a21];no original open-list reordering

Conditions: none

Intersect every declared neighborhood to form a candidate,without yet assuming a topology.Retain the original open-list order;only set elements use UTF16 sorting.

Step identifiers and dependencies

Rule: compactclosed_ALL_given_neighborhood_intersection_candidates · Uses: G001, S001

S003 · implies

Before

ORIGINAL carrier order=[a21, b21, c21];ORIGINAL open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []];point=b21;ALL given sets containing it have indices=[0, 1, 4, 5]

After

candidate N(b21)=intersection of ALL those sets=[b21];no original open-list reordering

Conditions: none

Intersect every declared neighborhood to form a candidate,without yet assuming a topology.Retain the original open-list order;only set elements use UTF16 sorting.

Step identifiers and dependencies

Rule: compactclosed_ALL_given_neighborhood_intersection_candidates · Uses: G001, S002

S004 · implies

Before

ORIGINAL carrier order=[a21, b21, c21];ORIGINAL open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []];point=c21;ALL given sets containing it have indices=[0, 2, 4, 6]

After

candidate N(c21)=intersection of ALL those sets=[c21];no original open-list reordering

Conditions: none

Intersect every declared neighborhood to form a candidate,without yet assuming a topology.Retain the original open-list order;only set elements use UTF16 sorting.

Step identifiers and dependencies

Rule: compactclosed_ALL_given_neighborhood_intersection_candidates · Uses: G001, S003

S005 · implies

Before

ORIGINAL ordered open masks=[7, 3, 5, 1, 6, 2, 4, 0];ALL neighborhood-containment [x,y,N(y)_subset_N(x)] rows=[[a21, a21, Yes], [b21, b21, Yes], [c21, c21, Yes]]

After

ALL carrier masks0..7 audited;EXACT qualifying U with every x in U having N(x) subset U=[0, 1, 2, 3, 4, 5, 6, 7];given family equals this COMPLETE upset family

Conditions: none

In a finite topology,opens are exactly upsets of its minimal neighborhoods.Conversely,after comparing every carrier subset,upsets are closed under arbitrary unions and finite intersections and contain empty/full sets,so this is a topology with open N(x).This covers all closure obligations,not sampled pairs,without printing millions of pairs.

Step identifiers and dependencies

Rule: compactclosed_ALL_carrier_subsets_exact_neighborhood_upsets_topology · Uses: G001, S004

S006 · implies

Before

Compact-closed ORIGINAL pair index0-1:ORIGINAL distinct x=a21,y=b21;N(y)=[b21];open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []]

After

ALL tested [U_index,U_intersect_N(y),disjoint_V_possible] rows=[[0, [b21], No], [1, [b21], No], [2, [], Yes]];for FIRST possible U,ALL tested [V_index,intersection,disjoint] rows=[[0, [a21, c21], No], [1, [a21], No], [4, [c21], No], [5, [], Yes]];FIRST ORIGINAL witness=[[a21, c21], [b21]]

Conditions: none

If U meets N(y),every open containing y also meets U.If disjoint,N(y) itself is an available open,then search original V order for the first witness.This preserves exactly the original full U/V search result,not an alternate minimal-neighborhood answer.

Step identifiers and dependencies

Rule: compactclosed_FIRST_original_separator_with_complete_neighborhood_screen · Uses: G001, S005

S007 · implies

Before

Compact-closed ORIGINAL pair index0-2:ORIGINAL distinct x=a21,y=c21;N(y)=[c21];open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []]

After

ALL tested [U_index,U_intersect_N(y),disjoint_V_possible] rows=[[0, [c21], No], [1, [], Yes]];for FIRST possible U,ALL tested [V_index,intersection,disjoint] rows=[[0, [a21, b21], No], [2, [a21], No], [4, [b21], No], [6, [], Yes]];FIRST ORIGINAL witness=[[a21, b21], [c21]]

Conditions: none

If U meets N(y),every open containing y also meets U.If disjoint,N(y) itself is an available open,then search original V order for the first witness.This preserves exactly the original full U/V search result,not an alternate minimal-neighborhood answer.

Step identifiers and dependencies

Rule: compactclosed_FIRST_original_separator_with_complete_neighborhood_screen · Uses: G001, S006

S008 · implies

Before

Compact-closed ORIGINAL pair index1-2:ORIGINAL distinct x=b21,y=c21;N(y)=[c21];open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []]

After

ALL tested [U_index,U_intersect_N(y),disjoint_V_possible] rows=[[0, [c21], No], [1, [], Yes]];for FIRST possible U,ALL tested [V_index,intersection,disjoint] rows=[[0, [a21, b21], No], [2, [a21], No], [4, [b21], No], [6, [], Yes]];FIRST ORIGINAL witness=[[a21, b21], [c21]]

Conditions: none

If U meets N(y),every open containing y also meets U.If disjoint,N(y) itself is an available open,then search original V order for the first witness.This preserves exactly the original full U/V search result,not an alternate minimal-neighborhood answer.

Step identifiers and dependencies

Rule: compactclosed_FIRST_original_separator_with_complete_neighborhood_screen · Uses: G001, S007

S009 · implies

Before

ORIGINAL points=[a21, b21, c21];ALL original-index distinct-pair witnesses=[[a21, b21, [[a21, c21], [b21]]], [a21, c21, [[a21, b21], [c21]]], [b21, c21, [[a21, b21], [c21]]]];actual K=[a21, b21]

After

Hausdorff=Yes;K compact=Yes by finiteness:from ANY cover choose one member per K point;empty K needs no members;ambient complement=[c21],closed=Yes

Conditions: none

Finite K compactness does not replace ambient Hausdorffness.An empty pair domain is vacuous.Closedness tests the complement in this same ambient space,not a relative complement.

Step identifiers and dependencies

Rule: compactclosed_ALL_pairs_Hausdorff_and_finite_subset_compact_separate · Uses: G001, S008

S010 · implies

Before

CURRENT ambient Hausdorff=Yes;compact K=[a21, b21];consider ANY exterior x

After

for EACH y in K choose disjoint opens U_y containing x,V_y containing y;the V_y cover K;compactness picks FINITELY MANY indices;their U_y intersection is open,contains x and avoids ALL K,so X minus K is open

Conditions: none

The general theorem uses compactness to select a finite subcover,not numbers from this finite model.Each K point lies in a selected V disjoint from its corresponding U;the finite intersection therefore avoids all K.For empty K,the empty intersection is X.No converse closed-implies-compact is claimed.

Step identifiers and dependencies

Rule: compactclosed_GENERAL_Hausdorff_finite_subcover_intersection_proof · Uses: G001, S009

S011 · implies

Before

Compact-closed ORIGINAL exterior versus K index0:ORIGINAL distinct x=c21,y=a21;N(y)=[a21];open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []]

After

ALL tested [U_index,U_intersect_N(y),disjoint_V_possible] rows=[[0, [a21], No], [2, [a21], No], [4, [], Yes]];for FIRST possible U,ALL tested [V_index,intersection,disjoint] rows=[[0, [b21, c21], No], [1, [b21], No], [2, [c21], No], [3, [], Yes]];FIRST ORIGINAL witness=[[b21, c21], [a21]]

Conditions: none

If U meets N(y),every open containing y also meets U.If disjoint,N(y) itself is an available open,then search original V order for the first witness.This preserves exactly the original full U/V search result,not an alternate minimal-neighborhood answer.

Step identifiers and dependencies

Rule: compactclosed_FIRST_original_separator_with_complete_neighborhood_screen · Uses: G001, S010

S012 · implies

Before

Compact-closed ORIGINAL exterior versus K index1:ORIGINAL distinct x=c21,y=b21;N(y)=[b21];open-list order=[[a21, b21, c21], [a21, b21], [a21, c21], [a21], [b21, c21], [b21], [c21], []]

After

ALL tested [U_index,U_intersect_N(y),disjoint_V_possible] rows=[[0, [b21], No], [2, [], Yes]];for FIRST possible U,ALL tested [V_index,intersection,disjoint] rows=[[0, [a21, c21], No], [1, [a21], No], [4, [c21], No], [5, [], Yes]];FIRST ORIGINAL witness=[[a21, c21], [b21]]

Conditions: none

If U meets N(y),every open containing y also meets U.If disjoint,N(y) itself is an available open,then search original V order for the first witness.This preserves exactly the original full U/V search result,not an alternate minimal-neighborhood answer.

Step identifiers and dependencies

Rule: compactclosed_FIRST_original_separator_with_complete_neighborhood_screen · Uses: G001, S011

S013 · implies

Before

ORIGINAL exterior x=c21;sorted K=[a21, b21];ALL [y,FIRST original separator]= [[a21, [[b21, c21], [a21]]], [b21, [[a21, c21], [b21]]]]

After

finite intersection of U sides=[c21];union of V sides=[a21, b21];covers K=Yes;intersection avoids K=Yes;intersection open=Yes

Conditions: none

The V union may exceed K while still covering it.The U intersection must be open,contain x and avoid K.No minimum/unique subcover is claimed;for empty K retain the raw carrier order in the empty intersection.

Step identifiers and dependencies

Rule: compactclosed_ACTUAL_cover_union_finite_U_intersection_original_order · Uses: G001, S012

Reverse checks

  • 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 — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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 — 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 — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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 — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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 — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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

(c21, [[a21, [[b21, c21], [a21]]], [b21, [[a21, c21], [b21]]]], [c21], [a21, b21], Yes, Yes, Yes, finite_subcover_and_finite_intersection_separate_x_from_K)

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: 8bc8717808fd627d19d194d7f5f1cdccd5f2a37dff29a32d296b9acb8cb49447
  • candidate record SHA-256: e07db479a77bc7bd861b1d32e299730390b0c644300808104a621b7cf3b60889
  • semantic review receipt SHA-256: a7c0d888ade6d307703c4222c4137c78c0d2448babdcba2fa3446fe6fdd343c1
  • question-first witness SHA-256: c9571f97a37d503ad6a61034cc00108543a05c37ef246d1c4962f55136a3de02
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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