### Abstract

This work presents a formalisation of a generating function proof for
Lucas's theorem. We first outline extensions to the existing
Formal Power Series (FPS) library, including an equivalence relation
for coefficients modulo

BSD License*n*, an alternate binomial theorem statement, and a formalised proof of the Freshman's dream (mod*p*) lemma. The second part of the work presents the formal proof of Lucas's Theorem. Working backwards, the formalisation first proves a well known corollary of the theorem which is easier to formalise, and then applies induction to prove the original theorem statement. The proof of the corollary aims to provide a good example of a formalised generating function equivalence proof using the FPS library. The final theorem statement is intended to be integrated into the formalised proof of Hilbert's 10th Problem.