enklesi fu'ivla

x1 is an (arbitrary) x2-set (li) of superset x3; x1 is subset/subgroup/subcategory/subclass/vel sim. of x3 with cardinality/size x2.

x1 is empty if(f) x2 = 0, which is possible; x1 may or may not be a proper substructure (praperi) of x3. x2 is a nonnegative cardinal. The two distinguishing features of x1 are its size (x2) and the object/structure (x3) to which it belongs/which contains it. Any x2 elements of x3 can belong to x1 as long as the total count is correct; no particular collection is necessarily included. It is bad form for x2 to strictly exceed the size/cardinality of x3 and, necessarily, no such object/structure can exist. See also: klesi, praperi, cletu.

In notes:

x1 is a strict/proper sub-x2 [structure] in/of x3; x2 is a structure and x1 and x3 are both examples of that structure x2 such that x1 is entirely contained within x3 (where containment is defined according to the standard/characteristics/definition of x2; but in any case, no member/part/element that belongs to x1 does not also belong to x3), but there is some member/part/element of x3 that does not belong to x1 in the same way.