(Forall (?Self ?Time)
(<=> (Active ?Time Substance-Container ?Self)
(And (Substance-Container ?Self)
(Active ?Time Structural-Element-Model ?Self))))
(=> (Substance-In $X $Y) (Substance-Container $X))
(Forall (?Self ?Time)
(<=> (Active ?Time Stream ?Self)
(And (Stream ?Self)
(Active ?Time Substance-Container ?Self))))
(Forall (?Self ?Time)
(<=> (Active ?Time Control-Volume ?Self)
(And (Control-Volume ?Self)
(Active ?Time Substance-Container ?Self))))
(=> (Contained-In $X $Y) (Substance-Container $Y))