Bruno Courcelle Cyril Gavoille Mamadou Moustapha Kanté Andrew Twigg Connectivity check in 3-connected planar graphs with obstacles. 151-155 2008 31 Electronic Notes in Discrete Mathematics http://dx.doi.org/10.1016/j.endm.2008.06.030 db/journals/endm/endm31.html#CourcelleGKT08