1. Higher Dimensional Algebra VII: Groupoidification;Baez,2010
2. Spans in 2-categories: A monoidal tricategoryhttp://arxiv.org/abs/1112.0560
3. Higher dimensional Algebra VIII: The Hecke bicategoryhttp://math.ucr.edu/home/baez/hecke.pdf
4. Quotients of the multiplihedron as categorified associahedrahttp://arxiv.org/PS_cache/arxiv/pdf/0803/0803.2694v4.pdf