Comment on the use of doubled surfaces
Graham P. Collins · Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields · 1989
I comment on a recent paper of Nagao and in particular give a proof that a special type of homology basis used by Nagao and previous workers is not admitted by the complex double of any unorientable surface with a boundary. However, their final results are not invalidated by the modifications required by the use of a less restricted class of homology bases.