 We may choose another way of giving meaning to programs, based on their execution. This operational interpretation is only defined on the set Prog of programs of \({L}\), and involves the definition of a suitable set of program values, which are the observables of \({L}\). If the execution of program \(e\) terminates with value \(v\), a situation expressed by the notation \(e \opDownarrow v\), then \(v\) is the operational meaning of \(e\). This defines the operational interpretation of programs as a partial function \({\mathcal{O}}\) from programs to values, where \({\mathcal{O}}(e) = v\) when \(e \opDownarrow v\).