Faster backtracking algorithms for the generation of symmetry-invariant permutations. Moreno, Oscar, Ramírez, John, Bollman, Dorothy, Orozco, Edusmildo (2002) Journal of Applied Mathematics
Flexibility of embeddings of bouquets of circles on the projective plane and Klein bottle. Yang, Yan, Liu, Yanpei (2007) The Electronic Journal of Combinatorics [electronic only]