15453 Formal Languages, Automata, and Computation
Lecture 23: Post Correspondence Problem
We complete the discussion of mapping reducibility by showing
that there are languages which are neither Turingrecognizable
nor coTuringrecognizable. We then introduce the Post Correspondence
Problem and prove that it is undecidable by a simple reduction
from the acceptance problem for Turing machines, using computation
histories.
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Frank Pfenning
