C. Barwick, and C. Schommer-Pries. (2011)cite http://arxiv.org/abs/1112.0040arxiv:1112.0040Comment: 46 pages, 2 figures. Corrections of a formatting error and addition of clearer acknowledgements.
J. Baez, and J. Dolan. (1997)cite http://arxiv.org/abs/q-alg/9702014arxiv:q-alg/9702014Comment: 59 pages LaTex, uses diagram.sty and auxdefs.sty macros, one encapsulated Postscript figure, also available as a compressed Postscript file at http://math.ucr.edu/home/baez/op.ps.Z or ftp://math.ucr.edu/pub/baez/op.ps.Z.