Euler’s Partition Theorem states that the number of partitions with only distinct parts is equal to the number of partitions with only odd parts. The combinatorial proof follows John Harrison’s pre-existing HOL Light formalization [1]. To understand the rough idea of the proof, I read the lecture notes of the MIT course 18.312 on Algebraic Combinatorics [2] by Gregg Musiker. This theorem is the 45th theorem of the Top 100 Theorems list. Contents 1 Additions to Isabelle’s Main Theories 2