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Question 21511: A Bounded Search No-Hit Is Not a Nonmembership Proof

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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R0042-21511 · q-20261014-advance-20261109-r07-context-free-grammar-0086

Original question and givens

Use the complete finite grammar: nonterminals=[S10, A10], terminals=[a10, b10], start=S10, productions=[[S10, [a10, A10]], [A10, [b10, A10]], [A10, []]] and allow_epsilon=true. Alphabets must be unique and disjoint, the start belongs to nonterminals, and each production [lhs,rhs] has exactly one nonterminal lhs and a finite legal-symbol rhs. Empty rhs is permitted only under the explicit epsilon convention. Keep original symbol and production order. Search word=[a10, b10] with max_steps=1. Give (word, max_steps, found_in_bounded_search, nonmembership_claim, boundary).

  • G001 — Use the complete finite grammar: nonterminals=[S10, A10], terminals=[a10, b10], start=S10, productions=[[S10, [a10, A10]], [A10, [b10, A10]], [A10, []]] and allow_epsilon=true. Alphabets must be unique and disjoint, the start belongs to nonterminals, and each production [lhs,rhs] has exactly one nonterminal lhs and a finite legal-symbol rhs. Empty rhs is permitted only under the explicit epsilon convention. Keep original symbol and production order. Search word=[a10, b10] with max_steps=1. Give (word, max_steps, found_in_bounded_search, nonmembership_claim, 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=cfg-bounded-search-boundary;original snapshot and mathematics retained

After

explicit ordered source output fields=[word, max_steps, found_in_bounded_search, nonmembership_claim, boundary]

Conditions: none

Keep the original historical interface marker while listing ordered source fields without JavaScript.Tags are not additional evidence;fixed No markers retain their source claim scope.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

ORIGINAL production index=0;lhs=S10,rhs=[a10, A10];N=[S10, A10],T=[a10, b10],allow_epsilon=Yes

After

lhs is ONE declared nonterminal;every rhs symbol legal;empty rhs accepted ONLY under the explicit epsilon convention;original production position retained

Conditions: none

Each production has one nonterminal on the left.Check every right-hand symbol and the explicit epsilon convention.Duplicate production positions may exist;sorting them would change first-witness indices.

Step identifiers and dependencies

Rule: cfg_each_original_production_single_nonterminal_legal_rhs · Uses: G001, S001

S003 · implies

Before

ORIGINAL production index=1;lhs=A10,rhs=[b10, A10];N=[S10, A10],T=[a10, b10],allow_epsilon=Yes

After

lhs is ONE declared nonterminal;every rhs symbol legal;empty rhs accepted ONLY under the explicit epsilon convention;original production position retained

Conditions: none

Each production has one nonterminal on the left.Check every right-hand symbol and the explicit epsilon convention.Duplicate production positions may exist;sorting them would change first-witness indices.

Step identifiers and dependencies

Rule: cfg_each_original_production_single_nonterminal_legal_rhs · Uses: G001, S002

S004 · implies

Before

ORIGINAL production index=2;lhs=A10,rhs=[];N=[S10, A10],T=[a10, b10],allow_epsilon=Yes

After

lhs is ONE declared nonterminal;every rhs symbol legal;empty rhs accepted ONLY under the explicit epsilon convention;original production position retained

Conditions: none

Each production has one nonterminal on the left.Check every right-hand symbol and the explicit epsilon convention.Duplicate production positions may exist;sorting them would change first-witness indices.

Step identifiers and dependencies

Rule: cfg_each_original_production_single_nonterminal_legal_rhs · Uses: G001, S003

S005 · implies

Before

ORIGINAL unique disjoint N=[S10, A10],T=[a10, b10];start=S10;complete productions=[[S10, [a10, A10]], [A10, [b10, A10]], [A10, []]];allow_epsilon=Yes

After

start belongs to nonterminals;finite grammar qualified;NO derivation,membership,regularity,unambiguity or PDA equivalence inferred

Conditions: none

Grammar qualification alone supplies no derivation for a word and no regularity or unambiguity claim.Retain both alphabet orders.

Step identifiers and dependencies

Rule: cfg_qualified_alphabets_start_not_language_property · Uses: G001, S004

S006 · implies

Before

ORIGINAL target form=[a10, b10];start=S10;max_steps=1;length cap=4

After

initial depth0 frontier=[[S10]];target already found=No;form equality itself does NOT require terminal-only target

Conditions: none

This is the declared depth-and-length-bounded search,not a general recognizer.Check exact form equality at depth0.A found form with nonterminals is not a terminal-word membership certificate.

Step identifiers and dependencies

Rule: cfg_bounded_search_initial_exact_form_not_terminal_membership · Uses: G001, S005

S007 · implies

Before

ORIGINAL depth=0;ALL frontier forms=[[S10]];length cap=4

After

ALL [from,position,production_index,next,target_equal,within_cap] transitions=[[[S10], 0, 0, [a10, A10], No, Yes]];next distinct frontier=[[a10, A10]];any hit=No

Conditions: none

Expand every legal position/production at this layer,deduplicating equal forms within the layer.Check target equality before the source length filter.Display sorting makes a set readable without altering production indices or existential found status.

Step identifiers and dependencies

Rule: cfg_every_bounded_frontier_expansion_and_length_filter · Uses: G001, S006

S008 · implies

Before

ORIGINAL target=[a10, b10],depth bound=1;bounded found=No

After

nonmembership_claim fixed No whether found or not;longer or excluded derivations have NOT been ruled out

Conditions: none

A no-hit rules out only paths within these depth/length limits.Without a completeness bound it is not a nonmembership proof.A found terminal string can separately witness membership,but not unambiguity.

Step identifiers and dependencies

Rule: cfg_bounded_nohit_never_nonmembership_claim · Uses: G001, S007

Reverse checks

  • 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

([a10, b10], 1, No, No, bounded_search_failure_cannot_prove_nonmembership_without_complete_bound)

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: 24cc6312247716af31d2c232260cd008c2523b9549ca9c4dd917df17b5df3c8d
  • candidate record SHA-256: 706832662484c6c6f24faab32275e570d70c219f38158dd250162eb195d5c2cf
  • semantic review receipt SHA-256: dd44555041dfbb6fe9936aa00b9a5f8c5982c2784ef61dd0cbd5d1a303a49c1a
  • question-first witness SHA-256: 9a6011263f6ac53b9a1fd57addf2f3e2f6088b54802c539f332d689480dc2d17
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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