**Defined in theory: Quantity-spaces****Source code: quantity-spaces.lisp**

**Documentation:**A quantity-space is a set that has the property that a distance function is defined for any two elements in the set. In addition, the range of the distance function is a subclass of the class of scalar quantities.

**Subclass-Of:**Set

(<=> (Quantity-Space ?S) (And (Set ?S) (Forall (?X1 ?X2) (=> (And (Member ?X1 ?S) (Member ?X2 ?S)) (Exists (?D) (And (= ?D (Distance ?X1 ?X2)) (Scalar-Quantity ?D)))))))