By Achim D. Brucker and Amy Stell.
Deep learning, i.e., machine learning using neural networks, is used successfully in many application areas. Still, their use in safety-critical or security-critical applications is limited, due to the lack of testing and verification techniques. We address this problem by formalizing an important class of neural networks, feed-forward neural networks, in Isabelle/HOL. We present two different approaches of formalizing feed-forward networks and show their equivalence as well as demonstrate their use in verifying certain safety and correctness properties of various example. Moreover, we do not only provide a formal model that allows to reason over feed-forward neural networks, we also provide a datatype package for Isabelle/HOL that supports importing models from TensorFlow.js.
Please cite this work as follows: A. D. Brucker and A. Stell, “Formalizing neural networks,” Archive of Formal Proofs, 2025. https://isa-afp.org/entries/Neural_Networks.html, Formal proof development
@Article{ brucker.ea:afp-neural_networks:2025,
author = {Achim D. Brucker and Amy Stell},
title = {Formalizing Neural Networks},
journal = {Archive of Formal Proofs},
areas = {security, software},
month = {November},
year = {2025},
note = {\url{https://isa-afp.org/entries/Neural_Networks.html},
Formal proof development},
issn = {2150-914x},
abstract = {Deep learning, i.e., machine learning using neural networks,
is used successfully in many application areas. Still, their
use in safety-critical or security-critical applications is
limited, due to the lack of testing and verification
techniques. We address this problem by formalizing an
important class of neural networks, feed-forward neural
networks, in Isabelle/HOL. We present two different approaches
of formalizing feed-forward networks and show their
equivalence as well as demonstrate their use in verifying
certain safety and correctness properties of various example.
Moreover, we do not only provide a formal model that allows to
reason over feed-forward neural networks, we also provide a
datatype package for Isabelle/HOL that supports importing
models from TensorFlow.js.},
}