RT Book, Whole DB /z-wcorg/ DS http://worldcat.org ID 227469361 LA English T1 New proofs of old theorems in logic and formal linguistics. A1 Floyd, Robert W., CARNEGIE INST OF TECH PITTSBURGH PA., PB Defense Technical Information Center PP Ft. Belvoir YR 1966 AB 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).