Definition 2.1 in Rafi S., Padgett, J.L., Nakarmi, U. (2024) Towards an Algebraic Framework For
Approximating Functions Using Neural Network Polynomials
https://arxiv.org/abs/2402.01058
Which in turn is a modified version of the one found in:
Definition 2.3. Grohs, P., Hornung, F., Jentzen, A. et al.
Space-time error estimates for deep neural network approximations
for differential equations. (2019).
https://arxiv.org/abs/1908.03833.