© 1977 by London Mathematical Society
Antipodal Embeddings of Graphs
Department of Pure Mathematics, University College of Swansea Swansea, SA2 8PP, Great Britain
An antipodal graph D of diameter d has the property that each vertex
has a unique (antipodal) vertex
at distance d from
in D. We show that any such D has circuits of length 2d passing through antipodal pairs of vertices. The identification of antipodal vertex-pairs in D produces a quotient graph G with a double cover projection morphism p : D
G. Using the two-fold quotient map of surfaces
: S2
RP2 where the real projective plane is obtained from the sphere, we study the relation between embeddings of a planar graph in S2 and embeddings of G in RP2. In particular, our main theorem establishes that every planar antipodal graph D has an embedding in S2 such that p is a restriction of the projection
.