Decidability and Undecidability of Marked PCP

We show that the marked version of the Post Correspondence Problem, where the words on a list are required to di er in the rst letter, is decidable. On the other hand, PCP remains undecidable if we only require the words to di er in the rst two letters. Thus we locate the decidability/undecidability-boundary between marked and 2-marked PCP.

• Type: Conference
• Year: 1999
• Where: STACS
• Authors: Vesa Halava, Mika Hirvensalo, Ronald de Wolf
• Keywords: Marked Version, Post Correspondence Problem, Rst Letter, STACS 1999, Theoretical Computer Science