  We present a fully abstract model of a call-by-value language with
higher-order functions, recursion and natural numbers, as an exponential ideal
in a topos. Our model is inspired by the fully abstract models of O'Hearn,
Riecke and Sandholm, and Marz and Streicher. In contrast with semantics based
on cpo's, we treat recursion as just one feature in a model built by combining
a choice of modular components.
