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Question 18961: Revisiting Vertices Is Allowed; Repeating an Edge Is Not

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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R0036-18961 · q-20261014-advance-20261105-r04-eulerian-trail-0011

Original question and givens

Use the complete finite simple undirected graph on Fin(13)={0,…,12}, with canonical sorted edges=[[0, 1], [0, 12], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9], [9, 10], [10, 11], [11, 12]] and zero-based edge indices in that order. The edge support contains exactly the nonisolated vertices. A trail may revisit vertices but may not repeat an edge; an Euler trail uses every edge once. Isolated vertices do not invalidate connected edge support, and no Hamiltonian conclusion follows. Supplied vertex_walk=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0]. Give (vertex_walk, used_edge_indices, length_and_adjacency, recorded_edge_indices_unique, recorded_edges_cover_exactly_once, vertex_revisited, valid_euler_trail, boundary).

  • G001 — Use the complete finite simple undirected graph on Fin(13)={0,…,12}, with canonical sorted edges=[[0, 1], [0, 12], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9], [9, 10], [10, 11], [11, 12]] and zero-based edge indices in that order. The edge support contains exactly the nonisolated vertices. A trail may revisit vertices but may not repeat an edge; an Euler trail uses every edge once. Isolated vertices do not invalidate connected edge support, and no Hamiltonian conclusion follows. Supplied vertex_walk=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0]. Give (vertex_walk, used_edge_indices, length_and_adjacency, recorded_edge_indices_unique, recorded_edges_cover_exactly_once, vertex_revisited, valid_euler_trail, boundary).

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=euler-trail-audit;original snapshot and mathematics retained

After

explicit ordered source output fields=[vertex_walk, used_edge_indices, length_and_adjacency, recorded_edge_indices_unique, recorded_edges_cover_exactly_once, vertex_revisited, valid_euler_trail, boundary]

Conditions: none

Keep the historical interface marker in the original snapshot while listing the original ordered fields here.No JavaScript or external table is needed for the main text,and field labels are not mathematical evidence.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

complete ORIGINAL carrier Fin(13);canonical ORIGINAL simple undirected edges=[[0, 1], [0, 12], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9], [9, 10], [10, 11], [11, 12]]

After

edge indices are EXACT original list positions0..12;retain ALL vertices;no12-vertex or10-edge bound

Conditions: none

Keep edge indices at their original numeric positions,not string-sorted vertex pairs.This family permits up to60 vertices rather than importing earlier bounds;empty-edge graphs appear only where the operation allows them.

Step identifiers and dependencies

Rule: euler_original_simple_graph_indices_full_carrier · Uses: G001, S001

S003 · implies

Before

original walk step=0;consecutive vertices=[0, 1];undirected candidate edge=[0, 1]

After

matching original edge index=0;recorded edge prefix=[0];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S002

S004 · implies

Before

original walk step=1;consecutive vertices=[1, 2];undirected candidate edge=[1, 2]

After

matching original edge index=2;recorded edge prefix=[0, 2];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S003

S005 · implies

Before

original walk step=2;consecutive vertices=[2, 3];undirected candidate edge=[2, 3]

After

matching original edge index=3;recorded edge prefix=[0, 2, 3];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S004

S006 · implies

Before

original walk step=3;consecutive vertices=[3, 4];undirected candidate edge=[3, 4]

After

matching original edge index=4;recorded edge prefix=[0, 2, 3, 4];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S005

S007 · implies

Before

original walk step=4;consecutive vertices=[4, 5];undirected candidate edge=[4, 5]

After

matching original edge index=5;recorded edge prefix=[0, 2, 3, 4, 5];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S006

S008 · implies

Before

original walk step=5;consecutive vertices=[5, 6];undirected candidate edge=[5, 6]

After

matching original edge index=6;recorded edge prefix=[0, 2, 3, 4, 5, 6];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S007

S009 · implies

Before

original walk step=6;consecutive vertices=[6, 7];undirected candidate edge=[6, 7]

After

matching original edge index=7;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S008

S010 · implies

Before

original walk step=7;consecutive vertices=[7, 8];undirected candidate edge=[7, 8]

After

matching original edge index=8;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7, 8];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S009

S011 · implies

Before

original walk step=8;consecutive vertices=[8, 9];undirected candidate edge=[8, 9]

After

matching original edge index=9;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7, 8, 9];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S010

S012 · implies

Before

original walk step=9;consecutive vertices=[9, 10];undirected candidate edge=[9, 10]

After

matching original edge index=10;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7, 8, 9, 10];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S011

S013 · implies

Before

original walk step=10;consecutive vertices=[10, 11];undirected candidate edge=[10, 11]

After

matching original edge index=11;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S012

S014 · implies

Before

original walk step=11;consecutive vertices=[11, 12];undirected candidate edge=[11, 12]

After

matching original edge index=12;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S013

S015 · implies

Before

original walk step=12;consecutive vertices=[12, 0];undirected candidate edge=[0, 12]

After

matching original edge index=1;recorded edge prefix=[0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1];length-and-adjacency status=Yes

Conditions: none

Look up every consecutive step in the original graph.A missing edge fails adjacency and is not added as a fake used index.The recorded list contains only found edges,so its coverage cannot replace complete walk validity.

Step identifiers and dependencies

Rule: euler_every_walk_step_missing_edge_not_recorded · Uses: G001, S014

S016 · implies

Before

original complete walk=[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0];required vertex-list length=14;actual length=14;found ORIGINAL edge indices=[0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1]

After

length-and-all-adjacency=Yes;recorded indices unique=Yes;recorded complete single-use coverage=Yes;vertex revisited=Yes;VALID Euler trail=Yes

Conditions: none

An Euler trail may revisit vertices but not edges.Final validity conjoins length/all-adjacency with complete single-use edge coverage.Extra missing steps can leave a recorded list that covers every edge while invalidating the walk.One bad supplied walk does not disprove existence of another Euler walk.

Step identifiers and dependencies

Rule: euler_trail_full_conjunction_repeated_vertices_permitted · Uses: G001, S015

Reverse checks

  • S016 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S015 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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 — 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

([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0], [0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 1], Yes, Yes, Yes, Yes, Yes, trail_allows_repeated_vertices_not_edges)

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: 65a6378c5bb876f30002628536aba4ed833767951399798f432aa98b1aed7861
  • candidate record SHA-256: e922e5c2ce22bfb732a6cf505b87f7ef66924fe0eabdde3a88544dad32b51047
  • semantic review receipt SHA-256: efee5462991619d6ed9f64f11ddb085e5614ef33f9f8fcd8cf29b9329f8fd301
  • question-first witness SHA-256: acf91fa1622f01d2cf04b2c513294254323665351f660f2628aaafdb869c4ff2
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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