$[\![z \subset \dot{x}]\!]=[\![z \subset \dot{x}]\!][\![z=\alpha]\!]=\dot{y}(z)[\![z=\alpha]\!] \leq [\![z=\alpha]\!][\![z\in\dot{y}]\!] \leq [\![\alpha \in \dot{y}]\!]$, isto é, $[\![z\subset \dot{x} \Longrightarrow \alpha \in \dot{y}]\!]=1$.