Possible($R$;${\it es}$)
\\[0ex]$\,\equiv$$_{\mbox{\scriptsize def}}$$\;\;$R{-}Feasible($R$) c$\wedge$ ($\exists$$w$:World. $\exists$$p$:FairFifo. (PossibleWorld([[$R$]];$w$) \& ${\it es}$ = ES($w$)))