x Abstract. We introduce an untyped-calculus with input-output, based on Gordon's continuation-passing model of input-output. This calculus is intended to allow the classiication of possibly innnite input-output behaviors, such as those required for servers or distributed systems. We deene two terms to be operationally approximate ii they have similar behaviors in any context. We then deene a notion of applicative approximation and show that it coincides with operational approximation for these… CONTINUE READING