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Question 24766: An Explicit Repeated Blank Configuration Proves This Recognizer Is Not a Decider

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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R0048-24766 · q-20261015-advance-20261113-r05-turing-machine-decision-model-0091

Original question and givens

Use deterministic single-tape states=[scan, accept, reject], input_alphabet=[a15, b15], tape_alphabet=[a15, b15, _], blank=_, start=scan, accept=accept, reject=reject, transitions=[[scan, a15, scan, a15, R], [scan, b15, accept, b15, S], [scan, _, scan, _, S]]. Each transition is [state,read,next,write,L/R/S]; keys [state,read] are unique and halting states have no outgoing transitions. Input symbols form a blank-free tape subset. The integer-indexed tape is blank at every unlisted cell, with configuration [state,head,sparse nonblank tape]; L may move left of0. Canonical answer transitions/tape cells retain the source sort convention. Target=b15, legal target-free input=[a15, a15]. Give (states, input_alphabet, tape_alphabet, transitions, target_symbol, input, loop_configuration, next_configuration, exact_self_loop, decider, boundary).

  • G001 — Use deterministic single-tape states=[scan, accept, reject], input_alphabet=[a15, b15], tape_alphabet=[a15, b15, _], blank=_, start=scan, accept=accept, reject=reject, transitions=[[scan, a15, scan, a15, R], [scan, b15, accept, b15, S], [scan, _, scan, _, S]]. Each transition is [state,read,next,write,L/R/S]; keys [state,read] are unique and halting states have no outgoing transitions. Input symbols form a blank-free tape subset. The integer-indexed tape is blank at every unlisted cell, with configuration [state,head,sparse nonblank tape]; L may move left of0. Canonical answer transitions/tape cells retain the source sort convention. Target=b15, legal target-free input=[a15, a15]. Give (states, input_alphabet, tape_alphabet, transitions, target_symbol, input, loop_configuration, next_configuration, exact_self_loop, decider, 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 roles = [tm-recognizer-loop-boundary]

After

derived = [[states, input_alphabet, tape_alphabet, transitions, target_symbol, input, loop_configuration, next_configuration, exact_self_loop, decider, boundary]]

Conditions: none

List the full source field order without JavaScript,keeping original data,Boolean flags,mathematical objects and nonclaims distinct.

Step identifiers and dependencies

Rule: source_ordered_fields_without_JS · Uses: G001

S002 · implies

Before

source roles = [[scan, accept, reject], [a15, b15], [a15, b15, _], _, scan, accept, reject, [[scan, a15, scan, a15, R], [scan, b15, accept, b15, S], [scan, _, scan, _, S]]]

After

derived = [[accept, reject, scan], [a15, b15], [_, a15, b15], [[scan, _, scan, _, S], [scan, a15, scan, a15, R], [scan, b15, accept, b15, S]], Yes]

Conditions: none

All three lists are nonempty and unique;input is a blank-free tape subset,but state and alphabet labels may overlap.Source NUL-joined(from,read) keys are unique,and halting states have no outgoing rules.A partial table is legal,not filled with rejection;transition collation and UTF16 set order differ.

Step identifiers and dependencies

Rule: TM_complete_signature_partial_transition_table_allowed · Uses: G001, S001

S003 · implies

Before

source roles = [b15, Yes, [[accept, reject, scan], [a15, b15], [_, a15, b15], _, scan, accept, reject, [[scan, _, scan, _, S], [scan, a15, scan, a15, R], [scan, b15, accept, b15, S]]]]

After

derived = [[[accept, reject, scan], [a15, b15], [_, a15, b15], _, scan, accept, reject, [[scan, _, scan, _, S], [scan, a15, scan, a15, R], [scan, b15, accept, b15, S]]], Yes]

Conditions: none

Require the exact full signature and all schema transitions;sample successful traces do not certify an arbitrary TM.

Step identifiers and dependencies

Rule: TM_EXACT_canonical_scan_schema_not_sampled_machine · Uses: G001, S002

S004 · implies

Before

source roles = [[a15, a15], b15, [[scan, _, scan, _, S], [scan, a15, scan, a15, R], [scan, b15, accept, b15, S]]]

After

derived = [[scan, 2, [[0, a15], [1, a15]]], [scan, 2, [[0, a15], [1, a15]]], Yes, No]

Conditions: none

Copy/R across every target-free input symbol reaches blank at head|w|.The blank rule writes blank,stays S and remains scan,so the entire configuration repeats.Determinism proves this input loops forever,refuting this recognizer as a decider,not by budget exhaustion.

Step identifiers and dependencies

Rule: TM_actual_target_free_input_reaches_EXACT_blank_SELFLOOP · Uses: G001, S003

Reverse checks

  • 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

([accept, reject, scan], [a15, b15], [_, a15, b15], [[scan, _, scan, _, S], [scan, a15, scan, a15, R], [scan, b15, accept, b15, S]], b15, [a15, a15], [scan, 2, [[0, a15], [1, a15]]], [scan, 2, [[0, a15], [1, a15]]], Yes, No, explicit_blank_self_loop_proves_this_recognizer_is_not_a_decider_on_the_target_free_input)

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: d088edd52ce7cf0dcc97a4c1044ce8e4474583048631e3211aa32e6add8ba23a
  • candidate record SHA-256: ba6ce04be03820d88dc5412c342d2e3a9d04c41245c23810ee05438ff19ece4d
  • semantic review receipt SHA-256: 049a9e07e69fead88d93b34f0937b9470a06d71c1a8d097058fc83554529bdd0
  • question-first witness SHA-256: 0c71ebb418f3de347d232d159fc25e93036f4ab9166bcfb5ee5b4be86d5c55b9
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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