Composition direction of Seymour's theorem for regular matroids — Formally verified
M. Dvorak, T. Figueroa-Reid, R. Hamadani, B.-H. Hwang, E. Karunus, V. Kolmogorov, A. Meiburg, A. Nelson, P. Nelson, M. Sandey, I. Sergeev, ArXiv (n.d.).