Lifts of pseudo-Anosov homeomorphisms of nonorientable surfaces have   vanishing SAF invariant
  We show that any pseudo-Anosov map that is a lift of pseudo-Anosov homeomorphism of a nonorientable surface has vanishing SAF invariant. We also provide a criterion to certify that a pseudo-Anosov map is not such a lift. 
Bal\'azs Strenner
math.GT math.DS