Complexity of a Problem Concerning Reset Words for Eulerian Binary   Automata
  A word is called a reset word for a deterministic finite automaton if it maps all the states of the automaton to a unique state. Deciding about the existence of a reset word of a given maximum length for a given automaton is known to be an NP-complete problem. We prove that it remains NP-complete even if restricted to Eulerian automata with binary alphabets, as it has been conjectured by Martyugin (2011). 
Vojt\v{e}ch Vorel
cs.FL