T-homotopy and refinement of observation. IV. Invariance of the underlying homotopy type. Gaucher, Philippe (2006) The New York Journal of Mathematics [electronic only]
Universal properties and derived Kan extensions. (Propriétés universelles et extensions de Kan dérivées.) Cisinski, Denis-Charles (2008) Theory and Applications of Categories [electronic only]
Weak cofibrations in categories of cofibrant objects. Kieboom, R.W., Sonck, G., Van der Linden, T., Witbooi, P.J. (2003) Homology, Homotopy and Applications
Weak subobjects and weak limits in categories and homotopy categories Marco Grandis (1997) Cahiers de Topologie et Géométrie Différentielle Catégoriques