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## Details

Document Type: | Book |
---|---|

All Authors / Contributors: |
Robert W Floyd; CARNEGIE INST OF TECH PITTSBURGH PA. |

OCLC Number: | 227469361 |

Notes: | Prepared in cooperation with Computer Associates, Inc., Auburn, Mass., Contract AF 30(602)-3342. |

Description: | 19 pages |

### Abstract:

Theorem 1 constructs, from any word problem in a semi-Thue system, an equivalent Post correspondence problem, showing the undecidability of the general Post correspondence problem. Theorem 2 constructs, from any Post correspondence problem, a minimal linear grammar which is ambiguous exactly if the Post correspondence problem has a solution, showing the undecidability of the general ambiguity problem. (Other standard undecidability results on phrase structure grammars are implied.) Theorem 3 constructs, from any word problem in a semi-Thue system, an ambiguity problem, combining the results of Theorem 1 and 2 by more direct means. No new results are presented, but standard proofs were shortened and constructions eliminated, combined, or simplified. (Author).

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