 Full abstraction also functions as a criterion for assessing a translation \(\vartheta\) from a language \({L}_1\) into a (not necessarily different) language \({L}_2\), provided the two languages have the same sets of observables, say Obs (Riecke 1993). Then \(\vartheta\) is fully abstract if observational equivalence (defined with respect to Obs) of \(e,e' \in {L}_1\) is equivalent to observational equivalence of \(\vartheta(e),\vartheta(e')\) in \({L}_2\). The existence of fully abstract translation between languages can be used to compare their expressive power, following a suggestion of (Mitchell 1993; Riecke 1993): \({L}_1\) is no more expressive than \({L}_2\) if there is a fully abstract translation of \({L}_1\) into \({L}_2\).