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Question 15534: Isolated Vertices Still Belong to Exactly One Part

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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R0030-15534 · q-20261014-advance-20261031-r02-bipartite-graph-0084

Original question and givens

Use the complete finite undirected loop-free simple graph on Fin(6)={0,…,5} with edges=[[0, 1], [1, 2], [2, 3], [3, 4]]. Normalize each edge increasingly, then sort edges lexicographically; reversed duplicates and loops are forbidden. Keep isolated vertices in the carrier. No directed-graph conclusion is inferred. The total part assignment=[0, 0, 0, 1, 0, 0] uses labels 0 or 1 for every vertex. Its two inverse-image parts are disjoint and cover the whole carrier. Every edge must cross parts; empty parts are allowed in an edgeless graph. Failure of this assignment alone does not prove the graph nonbipartite. vertex=5 must be isolated. Give (vertex,incident_edges,assigned_part,whole_partition_proper?,isolated_vertex_may_be_in_either_part_and_empty_part_allowed_for_edgeless_graph).

  • G001 — Use the complete finite undirected loop-free simple graph on Fin(6)={0,…,5} with edges=[[0, 1], [1, 2], [2, 3], [3, 4]]. Normalize each edge increasingly, then sort edges lexicographically; reversed duplicates and loops are forbidden. Keep isolated vertices in the carrier. No directed-graph conclusion is inferred. The total part assignment=[0, 0, 0, 1, 0, 0] uses labels 0 or 1 for every vertex. Its two inverse-image parts are disjoint and cover the whole carrier. Every edge must cross parts; empty parts are allowed in an edgeless graph. Failure of this assignment alone does not prove the graph nonbipartite. vertex=5 must be isolated. Give (vertex,incident_edges,assigned_part,whole_partition_proper?,isolated_vertex_may_be_in_either_part_and_empty_part_allowed_for_edgeless_graph).

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

complete undirected vertex carrier Fin(6);original edges=[[0, 1], [1, 2], [2, 3], [3, 4]]

After

normalized sorted simple edges=[[0, 1], [1, 2], [2, 3], [3, 4]];all vertices including isolates=[0, 1, 2, 3, 4, 5]

Conditions: none

Normalize endpoints and then sort edges lexicographically.Reversed duplicates are still duplicates and are rejected,as are loops.The complete carrier includes vertices absent from the edge list.

Step identifiers and dependencies

Rule: graph_complete_simple_carrier_normalized_edge_order · Uses: G001

S002 · implies

Before

total original part labels=[0, 0, 0, 1, 0, 0];complete carrier Fin(6)

After

part0=[0, 1, 2, 4, 5];part1=[3];disjoint full cover=Yes

Conditions: none

The two inverse images of0 and1 are disjoint and cover every originally labeled vertex.An empty part is allowed for an edgeless graph;isolates remain included.Edge crossing is still a separate obligation.

Step identifiers and dependencies

Rule: bipartition_total_inverse_image_parts · Uses: G001, S001

S003 · implies

Before

parts:normalized edge index=0;edge=[0, 1];endpoint labels=[0, 0]

After

different endpoints=No;same-label conflict=Yes

Conditions: none

Check the endpoints of each actual edge.Reused labels at nonadjacent vertices are not conflicts,and one crossing edge does not certify all other edges.

Step identifiers and dependencies

Rule: graph_every_edge_endpoint_constraint · Uses: G001, S002

S004 · implies

Before

parts:normalized edge index=1;edge=[1, 2];endpoint labels=[0, 0]

After

different endpoints=No;same-label conflict=Yes

Conditions: none

Check the endpoints of each actual edge.Reused labels at nonadjacent vertices are not conflicts,and one crossing edge does not certify all other edges.

Step identifiers and dependencies

Rule: graph_every_edge_endpoint_constraint · Uses: G001, S003

S005 · implies

Before

parts:normalized edge index=2;edge=[2, 3];endpoint labels=[0, 1]

After

different endpoints=Yes;same-label conflict=No

Conditions: none

Check the endpoints of each actual edge.Reused labels at nonadjacent vertices are not conflicts,and one crossing edge does not certify all other edges.

Step identifiers and dependencies

Rule: graph_every_edge_endpoint_constraint · Uses: G001, S004

S006 · implies

Before

parts:normalized edge index=3;edge=[3, 4];endpoint labels=[1, 0]

After

different endpoints=Yes;same-label conflict=No

Conditions: none

Check the endpoints of each actual edge.Reused labels at nonadjacent vertices are not conflicts,and one crossing edge does not certify all other edges.

Step identifiers and dependencies

Rule: graph_every_edge_endpoint_constraint · Uses: G001, S005

S007 · implies

Before

original vertex=5;all complete graph edges=[[0, 1], [1, 2], [2, 3], [3, 4]];assigned part=0

After

all incident edges=[];whole partition proper=No;isolate stays in exactly one part

Conditions: none

Only after checking no incident edges may this isolate be put in either part.It remains in the complete carrier with exactly one label.Changing it neither affects edge constraints nor repairs unrelated conflicts.

Step identifiers and dependencies

Rule: bipartite_isolated_vertex_not_omitted_or_whole_graph_fixed · Uses: G001, S006

Reverse checks

  • 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

(5, [], 0, No, isolated_vertex_may_be_in_either_part_and_empty_part_allowed_for_edgeless_graph)

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: ac076e7842bc7eb12b0fdf5dc7fbdc500f65058f57188cf37ff873a5c59288a4
  • candidate record SHA-256: e7ca74544bb0a0f95f6e0e0d027acaac17cfdd6f9548e32b5d4d90b88fa4e1f9
  • semantic review receipt SHA-256: 73bc08066ffb1a81eacb2d4e288d03f522aeefd3949fa0d97da41b484ed737bc
  • question-first witness SHA-256: ac120452a208b257b8270f38351a09dcd832cdbc8d9db6b69933f83e43cc9336
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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