Full abstraction and universality via realisability

We construct fully abstract realisability models of PCF. In particular, we prove a variant of the Longley-Phoa Conjecture by showing that the realisability model over an untyped /spl lambda/-calculus with arithmetic is fully abstract for PCF. Further we consider the extension of our results to a general sequential functional programming language SFPL giving rise to universal realisability models for SFPL.