 The basic papers on full abstraction for PCF are Milner 1977; Plotkin 1977. They can be read together as giving a coherent picture of the semantic analysis of this language. An independent approach to full abstraction came from the Russian logician Vladimir Sazonov who characterized definability in PCF in terms of a certain class of sequential computational strategies (Sazonov 1975, 1976). His work, however, had no direct influence on the bulk of research on the full abstraction problem, and only recently there have been attempts to relate Sazonov’s characterization to the game theoretic approaches (Sazonov 2007).