1. Heterogeneous algebras;Birkhoff;J. Combin. Theory,1970
2. Set theory with type restrictions;de Bruijn,1975
3. Generalised algebraic theories and contextual categories;Cartmell,1978
4. The Logic of Topoi;Fourman,1977
5. Aspects of topoi;Freyd;Bull. Austral. Math. Soc.,1972