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Question 22439: A Bounded PDA No-Hit Cannot Certify Rejection

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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R0043-22439 · q-20261014-advance-20261110-r07-pushdown-automaton-0089

Original question and givens

Use the complete finite nondeterministic PDA: states=[push13, pop13, accept13], input_alphabet=[a13, b13], stack_alphabet=[Z13, A13], start_state=push13, bottom_symbol=Z13, final_states=[accept13], transitions=[[push13, a13, Z13, push13, [Z13, A13]], [push13, a13, A13, push13, [A13, A13]], [push13, b13, A13, pop13, []], [pop13, b13, A13, pop13, []], [push13, null, Z13, accept13, [Z13]], [pop13, null, Z13, accept13, [Z13]]]. Alphabets are unique and pairwise disjoint. Each transition is [from,input symbol or null,required top,to,replacement bottom-to-top]. null is epsilon and consumes no input. Configurations are [state,input position,stack] with bottom first and top last. Preserve the bottom marker and accept only after consuming the entire input in a final state, not by empty stack. Input=[a13, a13, b13, b13], max_steps=1. Give (input, max_steps, found_accepting_run, rejection_or_nonmembership_claim, boundary).

  • G001 — Use the complete finite nondeterministic PDA: states=[push13, pop13, accept13], input_alphabet=[a13, b13], stack_alphabet=[Z13, A13], start_state=push13, bottom_symbol=Z13, final_states=[accept13], transitions=[[push13, a13, Z13, push13, [Z13, A13]], [push13, a13, A13, push13, [A13, A13]], [push13, b13, A13, pop13, []], [pop13, b13, A13, pop13, []], [push13, null, Z13, accept13, [Z13]], [pop13, null, Z13, accept13, [Z13]]]. Alphabets are unique and pairwise disjoint. Each transition is [from,input symbol or null,required top,to,replacement bottom-to-top]. null is epsilon and consumes no input. Configurations are [state,input position,stack] with bottom first and top last. Preserve the bottom marker and accept only after consuming the entire input in a final state, not by empty stack. Input=[a13, a13, b13, b13], max_steps=1. Give (input, max_steps, found_accepting_run, rejection_or_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=pda-bounded-search-boundary;original snapshot and mathematics retained

After

explicit ordered source output fields=[input, max_steps, found_accepting_run, rejection_or_nonmembership_claim, boundary]

Conditions: none

Retain the historical interface marker and list ordered source fields without JavaScript.MVT fields come from the original mode,without padding or answer-shape inference.Tags and fixed No markers retain their claim scope.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · implies

Before

ORIGINAL transition index=0;[from,input_or_null,required_top,to,replacement_bottom_to_top]=[push13, a13, Z13, push13, [Z13, A13]];bottom=Z13

After

states/input/stack symbols legal;null input consumes0;top=bottom requires replacement first bottom,otherwise replacement contains NO bottom;ORIGINAL transition position retained

Conditions: none

Check each original transition's state,input and stack roles without mixing alphabets.Null is epsilon,not an input symbol.The stack is bottom-first/top-last:pop one top then append the replacement in its original order.Apply the declared bottom guard,not an invented stronger convention.

Step identifiers and dependencies

Rule: pda_EVERY_original_transition_roles_epsilon_bottom_guard · Uses: G001, S001

S003 · implies

Before

ORIGINAL transition index=1;[from,input_or_null,required_top,to,replacement_bottom_to_top]=[push13, a13, A13, push13, [A13, A13]];bottom=Z13

After

states/input/stack symbols legal;null input consumes0;top=bottom requires replacement first bottom,otherwise replacement contains NO bottom;ORIGINAL transition position retained

Conditions: none

Check each original transition's state,input and stack roles without mixing alphabets.Null is epsilon,not an input symbol.The stack is bottom-first/top-last:pop one top then append the replacement in its original order.Apply the declared bottom guard,not an invented stronger convention.

Step identifiers and dependencies

Rule: pda_EVERY_original_transition_roles_epsilon_bottom_guard · Uses: G001, S002

S004 · implies

Before

ORIGINAL transition index=2;[from,input_or_null,required_top,to,replacement_bottom_to_top]=[push13, b13, A13, pop13, []];bottom=Z13

After

states/input/stack symbols legal;null input consumes0;top=bottom requires replacement first bottom,otherwise replacement contains NO bottom;ORIGINAL transition position retained

Conditions: none

Check each original transition's state,input and stack roles without mixing alphabets.Null is epsilon,not an input symbol.The stack is bottom-first/top-last:pop one top then append the replacement in its original order.Apply the declared bottom guard,not an invented stronger convention.

Step identifiers and dependencies

Rule: pda_EVERY_original_transition_roles_epsilon_bottom_guard · Uses: G001, S003

S005 · implies

Before

ORIGINAL transition index=3;[from,input_or_null,required_top,to,replacement_bottom_to_top]=[pop13, b13, A13, pop13, []];bottom=Z13

After

states/input/stack symbols legal;null input consumes0;top=bottom requires replacement first bottom,otherwise replacement contains NO bottom;ORIGINAL transition position retained

Conditions: none

Check each original transition's state,input and stack roles without mixing alphabets.Null is epsilon,not an input symbol.The stack is bottom-first/top-last:pop one top then append the replacement in its original order.Apply the declared bottom guard,not an invented stronger convention.

Step identifiers and dependencies

Rule: pda_EVERY_original_transition_roles_epsilon_bottom_guard · Uses: G001, S004

S006 · implies

Before

ORIGINAL transition index=4;[from,input_or_null,required_top,to,replacement_bottom_to_top]=[push13, null, Z13, accept13, [Z13]];bottom=Z13

After

states/input/stack symbols legal;null input consumes0;top=bottom requires replacement first bottom,otherwise replacement contains NO bottom;ORIGINAL transition position retained

Conditions: none

Check each original transition's state,input and stack roles without mixing alphabets.Null is epsilon,not an input symbol.The stack is bottom-first/top-last:pop one top then append the replacement in its original order.Apply the declared bottom guard,not an invented stronger convention.

Step identifiers and dependencies

Rule: pda_EVERY_original_transition_roles_epsilon_bottom_guard · Uses: G001, S005

S007 · implies

Before

ORIGINAL transition index=5;[from,input_or_null,required_top,to,replacement_bottom_to_top]=[pop13, null, Z13, accept13, [Z13]];bottom=Z13

After

states/input/stack symbols legal;null input consumes0;top=bottom requires replacement first bottom,otherwise replacement contains NO bottom;ORIGINAL transition position retained

Conditions: none

Check each original transition's state,input and stack roles without mixing alphabets.Null is epsilon,not an input symbol.The stack is bottom-first/top-last:pop one top then append the replacement in its original order.Apply the declared bottom guard,not an invented stronger convention.

Step identifiers and dependencies

Rule: pda_EVERY_original_transition_roles_epsilon_bottom_guard · Uses: G001, S006

S008 · calculation

Before

PDA complete ORIGINAL transition count := sum(1, 1, 1, 1, 1, 1)

After

PDA complete ORIGINAL transition count = 6

Conditions: none

Substitute original roles,order and established intermediates exactly,without changing source bindings or using floating-point approximations.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · implies

Before

ORIGINAL states=[push13, pop13, accept13],input alphabet=[a13, b13],stack alphabet=[Z13, A13];start=push13,bottom=Z13,final states=[accept13]

After

finite unique pairwise-disjoint alphabets qualified;transition count=6;acceptance convention FULL input in final state,NOT empty stack;qualification alone proves NO run,determinism or CFG equivalence

Conditions: none

A qualified complete definition gives no accepting run,determinism or CFG-equivalence proof.Acceptance may retain a nonempty stack,including its bottom,but requires full input consumption in a final state.

Step identifiers and dependencies

Rule: pda_complete_definition_not_determinism_or_accepting_run · Uses: G001, S008

S010 · implies

Before

ORIGINAL input=[a13, a13, b13, b13];initial configuration=[push13, 0, [Z13]];max_steps=1;stack cap=7

After

depth0 fully-consumed final-state acceptance=No;both STEP and STACK limits apply;not an unbounded rejection test

Conditions: none

The initial state may already accept empty input.Search bounds both steps and stack length;do not replace final-state acceptance with an empty-stack convention.

Step identifiers and dependencies

Rule: pda_bounded_initial_acceptance_and_TWO_search_limits · Uses: G001, S009

S011 · implies

Before

ORIGINAL search depth=0;ALL frontier configs=[[push13, 0, [Z13]]];stack cap=7

After

ALL [from,ORIGINAL transition index,next_or_null,within_stack_cap,accepts_IN_THIS_SEARCH] rows=[[[push13, 0, [Z13]], 0, [push13, 1, [Z13, A13]], Yes, No], [[push13, 0, [Z13]], 1, null, No, No], [[push13, 0, [Z13]], 2, null, No, No], [[push13, 0, [Z13]], 3, null, No, No], [[push13, 0, [Z13]], 4, [accept13, 0, [Z13]], Yes, No], [[push13, 0, [Z13]], 5, null, No, No]];next distinct frontier=[[accept13, 0, [Z13]], [push13, 1, [Z13, A13]]];hit=No

Conditions: none

Try every configuration and original transition.Filter candidates by the declared stack cap before testing acceptance in this search.Show the full layer rather than hidden pruning;within-layer deduplication preserves existence.

Step identifiers and dependencies

Rule: pda_ALL_nondeterministic_frontier_steps_stack_filter_BEFORE_acceptance · Uses: G001, S010

S012 · implies

Before

ORIGINAL input=[a13, a13, b13, b13];step bound=1;stack bound=7;found_accepting_run=No

After

rejection_or_nonmembership_claim fixed No;longer or larger-stack accepting runs have NOT been excluded

Conditions: none

A found run witnesses this bounded search;failure does not show that all runs reject.The final No does not negate a true found flag.No determinism or CFG equivalence is inferred.

Step identifiers and dependencies

Rule: pda_bounded_nohit_NOT_rejection_or_nonmembership · Uses: G001, S011

Reverse checks

  • 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 — Recompute PDA complete ORIGINAL transition count with exact rational arithmetic, not rounded decimals.
  • 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

([a13, a13, b13, b13], 1, No, No, bounded_nondeterministic_search_failure_cannot_prove_rejection_or_nonmembership)

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: 25d90e8026cda548792b30ba450f32267899c620c070e5367b23c3b2d5909c60
  • candidate record SHA-256: 788c9b7f8fa5c017997cffd3892bdbaf100252018df935412ca265bde30e0167
  • semantic review receipt SHA-256: 49cf6ec60211c92d1c0c302663af4d44479635dc8181fb61a20c3374288e21c5
  • question-first witness SHA-256: 10fd25b4643e5ff12753daceaa61f9f2499bf381f65ef96e9d21185c7c0d0c5e
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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