Explore related knowledge and questions →

Question 18426: Counting n−1 Edges Alone Does Not Establish a Tree

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

Return to catalogue page 93

← Question derivation index · Original question batch

R0035-18426 · q-20261014-advance-20261104-r06-spanning-tree-0026

Original question and givens

Use the complete finite undirected loop-free simple parent graph on Fin(5)={0,…,4}, canonical sorted edges=[[0, 1], [1, 2], [2, 3], [3, 4]], and distinct parent-edge selection=[0, 1, 2, 3], sorted increasingly. The selected subgraph retains every parent vertex, including isolated vertices. Audit parent connectivity, selected connectivity and acyclicity separately. A spanning tree is connected and acyclic on that full carrier; n−1 selected edges alone do not suffice. No edge weights or minimum-weight objective are supplied. Give (vertex_count, selected_edge_count, connected, acyclic, edge_count_is_n_minus_one, spanning_tree, boundary).

  • G001 — Use the complete finite undirected loop-free simple parent graph on Fin(5)={0,…,4}, canonical sorted edges=[[0, 1], [1, 2], [2, 3], [3, 4]], and distinct parent-edge selection=[0, 1, 2, 3], sorted increasingly. The selected subgraph retains every parent vertex, including isolated vertices. Audit parent connectivity, selected connectivity and acyclicity separately. A spanning tree is connected and acyclic on that full carrier; n−1 selected edges alone do not suffice. No edge weights or minimum-weight objective are supplied. Give (vertex_count, selected_edge_count, connected, acyclic, edge_count_is_n_minus_one, spanning_tree, 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=spantree-n-minus-one-certificate;original snapshot and mathematics retained

After

explicit ordered source output fields=[vertex_count, selected_edge_count, connected, acyclic, edge_count_is_n_minus_one, spanning_tree, boundary]

Conditions: none

Keep the historical interface marker in the original snapshot while giving ordered fields here,without JavaScript or an external table.Labels are not mathematical evidence,and each No marker retains the operation's claim scope.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

complete original vertex carrier Fin(5);canonical original edges=[[0, 1], [1, 2], [2, 3], [3, 4]];raw selected edge indices=[0, 1, 2, 3]

After

sorted unique ORIGINAL selection=[0, 1, 2, 3];selected edges=[[0, 1], [1, 2], [2, 3], [3, 4]];ALL parent vertices retained;no10-edge cap or weights

Conditions: none

This family bounds vertices by12 but has no maximum-matching10-edge cap.Select only original edges,retain every vertex including isolates,and normalize selection order without changing original indices.No weights or minimization objective are supplied.

Step identifiers and dependencies

Rule: spantree_original_graph_whole_carrier_not_matching_domain · Uses: G001, S001

S003 · implies

Before

parent graph:actual edge index=0;edge=[0, 1];reached from=0;new vertex=1

After

original-edge path from0=[0, 1];reached vertices=[0, 1]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S002

S004 · implies

Before

parent graph:actual edge index=1;edge=[1, 2];reached from=1;new vertex=2

After

original-edge path from0=[0, 1, 2];reached vertices=[0, 1, 2]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S003

S005 · implies

Before

parent graph:actual edge index=2;edge=[2, 3];reached from=2;new vertex=3

After

original-edge path from0=[0, 1, 2, 3];reached vertices=[0, 1, 2, 3]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S004

S006 · implies

Before

parent graph:actual edge index=3;edge=[3, 4];reached from=3;new vertex=4

After

original-edge path from0=[0, 1, 2, 3, 4];reached vertices=[0, 1, 2, 3, 4]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S005

S007 · implies

Before

parent graph:complete carrier Fin(5);ALL graph edges=[[0, 1], [1, 2], [2, 3], [3, 4]];reached=[0, 1, 2, 3, 4];unreached=[]

After

every graph edge stays within reached or its complement;connected=Yes

Conditions: none

After the queue is exhausted,no edge crosses the reached/unreached cut.Unreached vertices therefore have no path from0;otherwise path witnesses cover the carrier.A one-vertex empty-edge graph is connected via its initial vertex.

Step identifiers and dependencies

Rule: spantree_reachability_and_closed_cut_completeness · Uses: G001, S006

S008 · implies

Before

selected spanning subgraph:actual edge index=0;edge=[0, 1];reached from=0;new vertex=1

After

original-edge path from0=[0, 1];reached vertices=[0, 1]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S007

S009 · implies

Before

selected spanning subgraph:actual edge index=1;edge=[1, 2];reached from=1;new vertex=2

After

original-edge path from0=[0, 1, 2];reached vertices=[0, 1, 2]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S008

S010 · implies

Before

selected spanning subgraph:actual edge index=2;edge=[2, 3];reached from=2;new vertex=3

After

original-edge path from0=[0, 1, 2, 3];reached vertices=[0, 1, 2, 3]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S009

S011 · implies

Before

selected spanning subgraph:actual edge index=3;edge=[3, 4];reached from=3;new vertex=4

After

original-edge path from0=[0, 1, 2, 3, 4];reached vertices=[0, 1, 2, 3, 4]

Conditions: none

Each newly reached vertex has an actual-edge path from0;do not guess connectivity from counts.

Step identifiers and dependencies

Rule: spantree_every_discovered_vertex_path_witness · Uses: G001, S010

S012 · implies

Before

selected spanning subgraph:complete carrier Fin(5);ALL graph edges=[[0, 1], [1, 2], [2, 3], [3, 4]];reached=[0, 1, 2, 3, 4];unreached=[]

After

every graph edge stays within reached or its complement;connected=Yes

Conditions: none

After the queue is exhausted,no edge crosses the reached/unreached cut.Unreached vertices therefore have no path from0;otherwise path witnesses cover the carrier.A one-vertex empty-edge graph is connected via its initial vertex.

Step identifiers and dependencies

Rule: spantree_reachability_and_closed_cut_completeness · Uses: G001, S011

S013 · implies

Before

original selected edge index=0;edge=[0, 1];previous forest component roots=[0, 1]

After

closes cycle=No;actual cycle witness=[]

Conditions: none

If endpoints were already in the same forest component,the previous forest path plus this actual edge gives a cycle.Otherwise joining two components preserves acyclicity.Check every selected edge,not merely n−1 counts.

Step identifiers and dependencies

Rule: spantree_every_edge_cycle_or_forest_extension · Uses: G001, S012

S014 · implies

Before

original selected edge index=1;edge=[1, 2];previous forest component roots=[0, 2]

After

closes cycle=No;actual cycle witness=[]

Conditions: none

If endpoints were already in the same forest component,the previous forest path plus this actual edge gives a cycle.Otherwise joining two components preserves acyclicity.Check every selected edge,not merely n−1 counts.

Step identifiers and dependencies

Rule: spantree_every_edge_cycle_or_forest_extension · Uses: G001, S013

S015 · implies

Before

original selected edge index=2;edge=[2, 3];previous forest component roots=[0, 3]

After

closes cycle=No;actual cycle witness=[]

Conditions: none

If endpoints were already in the same forest component,the previous forest path plus this actual edge gives a cycle.Otherwise joining two components preserves acyclicity.Check every selected edge,not merely n−1 counts.

Step identifiers and dependencies

Rule: spantree_every_edge_cycle_or_forest_extension · Uses: G001, S014

S016 · implies

Before

original selected edge index=3;edge=[3, 4];previous forest component roots=[0, 4]

After

closes cycle=No;actual cycle witness=[]

Conditions: none

If endpoints were already in the same forest component,the previous forest path plus this actual edge gives a cycle.Otherwise joining two components preserves acyclicity.Check every selected edge,not merely n−1 counts.

Step identifiers and dependencies

Rule: spantree_every_edge_cycle_or_forest_extension · Uses: G001, S015

S017 · implies

Before

same complete vertex carrier Fin(5);parent connected=Yes;selected connected=Yes;all cycle witnesses=[]

After

selected acyclic=Yes;spanning tree validity=Yes

Conditions: none

A disconnected parent has no spanning tree,but failure of one selection in a connected parent does not refute existence of another.This audit retains all vertices and conjoins selected connectivity and acyclicity without dropping isolates.

Step identifiers and dependencies

Rule: spantree_connectivity_acyclicity_full_vertices_conjunction · Uses: G001, S016

S018 · calculation

Before

spanning tree vertex count minus one := sub(5, 1)

After

spanning tree vertex count minus one = 4

Conditions: none

Compute exactly from original roles and established intermediates,retaining indices,denominators,signs and the relevant carrier.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S017

S019 · implies

Before

ACTUAL vertex count=5;selected edge count=4;n-1=4;selected connected=Yes;acyclic=Yes

After

edge count matches=Yes;tree=Yes;n_minus_one_alone_insufficient

Conditions: none

A cycle plus an isolate can also have n−1 edges.This field compares counts only;tree validity still needs complete connectivity and acyclicity certificates.

Step identifiers and dependencies

Rule: spantree_edge_count_not_sufficient_alone · Uses: G001, S018

Reverse checks

  • S019 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S018 · premise_and_result_audit — Recompute spanning tree vertex count minus one with exact rational arithmetic, not rounded decimals.
  • S017 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • 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

(5, 4, Yes, Yes, Yes, Yes, n_minus_one_alone_insufficient)

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: b8e27be1cc67842179ce45c5d465b3a87f2a4a7448f3497c913dccfdf2645b95
  • candidate record SHA-256: 5eed51b17e8d9f30af79f851c2a64e7a8ac473290c048779210470f92302ae0a
  • semantic review receipt SHA-256: 713db6309b22bf8b31f0253d4aaa7aca9011ab908587ae0e9d4a365edce1f9bc
  • question-first witness SHA-256: 0338a3db344ab237113fc63be29153c3684da96e388109e9dcd913a0a693aed2
  • Lean: NOT_RUN · human review: NOT_PERFORMED
Same-source full JSON