Even Factors in Edge-Chromatic-Critical Graphs with a Small Number of Divalent Vertices
E. Steffen, I.H. Wolf, Graphs and Combinatorics 38 (2022).

Fractional Matchings, Component-Factors and Edge-Chromatic Critical Graphs
A. Klopp, E. Steffen, Graphs and Combinatorics (2021) 559–580.