Stable meet semilattice fibrations and free restriction categories. Cockett, J.R.B., Guo, Xiuzhan (2006) Theory and Applications of Categories [electronic only]
The catgorical theory of self-similarity. Hines, Peter (1999) Theory and Applications of Categories [electronic only]
The congruence class of an idempotent in a regular semigroup. M.E. Adams, M. Gould, S.T. Tschantz (1991) Semigroup forum