The sentence {tt (proper-subset $tau_1$ $tau_2$)} is true if the set denoted by $tau_1$ is a subset of the set denoted by $tau_2$ but not vice-versa.Notes:
- Source: KIF Version 3.0 Specification
(=> (Proper-Subset ?S1 ?S2) (Not (Subset ?S2 ?S1))) (=> (Proper-Subset ?S1 ?S2) (Subset ?S1 ?S2))
(<=> (Proper-Subset ?S1 ?S2) (And (Subset ?S1 ?S2) (Not (Subset ?S2 ?S1))))
(Exists (?U) (And (Bounded ?U) (Not (Empty ?U)) (Forall (?X) (=> (Member ?X ?U) (Exists (?Y) (And (Member ?Y ?U) (Proper-Subset ?X ?Y)))))))