1. IO and OI, DAIMIPB-47;Engelfnet,1975
2. Parameter passing mechanisms and nondeterminism;Hennessy;Proc. 9th Annual ACM Symposium on Theory of Computing,1977
3. Fixpoint approach to the theory of computation;Manna;Comm. ACM,1975
4. Models of LCF;Milner;Stanford Artificial Intelligence Laboratory Memo,1973