1. Aczel P. and N. Mendler, A Final Coalgebra Theorem, in: D. H. Pitt et al., editors, Category Theory and Computer Science. Proceedings 1989, Lecture Notes in Computer Science 389, Springer-Verlag, 1989 pp. 357–365.
2. “Models and Ultraproducts,”;Bell,1969
3. “Model Theory,”;Chang,1973
4. Goldblatt R., What is the Coalgebraic Analogue of Birkhoff's Variety Theorem?, Theoretical Computer Science, to appear. Manuscript available at http://www.mcs.vuw.ac.nz/~rob/papers/what.ps.
5. Hermida C., “Fibrations, Logical Predicates and Indeterminates,” Ph.D. thesis, University of Edinburgh (1993), techn. rep. LFCS-93-277. Also available as Aarhus Univ. DAIMI Techn. rep. PB-462.