X is a billiard ball. It is used as an example. It is considered to be homogeneous. While sticking to this example, it is good to have in mind (also) a more appropriate (but less familiar) example, namely that of a crystal (which may also be a crystal fragment) of the mineral quartz, as it occurs in the rock quartzite, which is aggregate of interlocked quartz crystals, that is, of contiguous quartz crystals.
X is individual (it is even an individual), so it satisfies [1] of Defintion 8 .
X does not involve inherence (provided we see X as an historical individual, implying that all replaceable determinations are removed), so it satisfies [2] of Defintion 8 .
X does not have a partition of it into mutually separable parts (there are no internal bona fide boundaries whatsoever, that is no internal boundaries that correspond to physical discontinuities), so it satisfies [3] of Defintion 8 .
(when X was a crystal of a quartzite, X could have a partition, namely as a result of its system of cleavage planes [if present at all]. But this is not a partition into separable parts.)
Consequently, X satisfies Definition 8, meaning that it is atomic, and thus satisfying [1] of Defintion 9 .
X is not specifically dependent on any other entity (which means that it is ontologically independent of any other entity, which indeed it is), so it satisfies [2] of Defintion 9 , and thus satisfies Definition 9, implying that X is substantial (It is the substantial member of the Substance-Accident duo, or, more generally, of the Mereo-totality (as carrier-only)-Accident duo).