**Defined in theory: Kif-sets****Source code: kif-sets.lisp**

**Documentation:**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.

**Arity:**2**Subrelation-Of:**Subset

(<=> (Proper-Subset ?S1 ?S2) (And (Subset ?S1 ?S2) (Not (Subset ?S2 ?S1))))

**Source:**KIF Version 3.0 Specification