How to mathematically represent the fact that electric charge is a fundamental quantity? i.e. that it cannot be explained in terms of other things, for example, the normal force can be explained as electrostatic repulsion thus it is not fundamental. However, Coulomb's law is fundamental since it can't be explained in any other terms.
For example, the mathematical equivalent of conservation and quantization of charge are as follows $$\vec\nabla\cdot\vec J+\frac{\partial\rho}{\partial t}=0$$ $$Q=ne,\, n\in \mathbb{Z} $$ So is there an analogous version for fundamental nature of charge?