Strengthening Hardness Results to 3-Connected Planar Graphs
  In this paper we extend some classical NP-hardness results from the class of 2-connected planar graphs to subclasses of 3-connected planar graphs. The reduction are partly based on a new graph augmentation, which may be of independent interest. 
Giordano Da Lozzo and Ignaz Rutter
cs.CC cs.CG math.CO