Mathematical structures, such as the presently discussed mathematical relations, do not possess individuals, they are ideal structures, which as such do not have a real, and thus no individual, existence.
These structures are real not until the symbols have a physical interpretation. If this is the case, then a symbol like Xn refers to say, a concentration of some given chemical substance. If such a chemical compound would be, in the present case, copper (Cu), then we could indicate this with the symbol Xn(Cu). The structure of the dynamical law then says something about a relevant qualitative aspect of copper, because a dynamical law is always inherent in the physical matter, that is, it is immanent, not transcendent ( The dynamical law is, as it were, composed of qualitative aspects of the system elements).