P. J. Ehlers and Tim Porter, Varieties of simplicial groupoids, I, Crossed complexes, Jour. Pure Applied Algebra, 120 (1997) 221 - 233; Erratum: Jour. Pure Applied Algebra, 134 (1999) 221-233.

P. J. Ehlers and Tim Porter, Ordinal subdivision and special pasting in quasicategories, Advances in Math. 217 (2007), No 2. pp 489-518.