An Infinite Class of Sparse-Yao Spanners
  We show that, for any integer k > 5, the Sparse-Yao graph YY_{6k} (also known as Yao-Yao) is a spanner with stretch factor 11.67. The stretch factor drops down to 4.75 for k > 7. 
Matthew Bauer and Mirela Damian
cs.CG cs.DS