 Clearly, the parallel-or function is not stable: the value \(\texttt{por}(\bot,{\textit{tt}}) = {\textit{tt}}= \texttt{por}({\textit{tt}},\bot)\) has no minimal producer. A remarkable property of stable functions is that they allow to build a new model of PCF, where \({{{D}^{\sigma \to \tau}}}\) is the set of stable functions on the domains that interpret the types \(\sigma\) and \(\tau\), which are refinements of Scott domains called dI-domains (Berry 1978). From our point of view, the important outcome of these definitions is the following adequacy result (Gunter 1992: chap. 6):