Dubouloz, A., Hedén, I. and Kishimoto, T. 2020. Equivariant extensions of $\mathbb{G}_a$-torsors over punctured surfaces . ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE. 21, special, 1-2 (Dec. 2020), 133-167. DOI:https://doi.org/10.2422/2036-2145.201710_002.