Variational metrics on 𝐑 × T M and the geometry of nonconservative mechanics Olga Krupková (1994) Mathematica Slovaca
Variational principle for the Finslerian extension of general relativity. G.S. Asanov (1982) Aequationes mathematicae
Variationsprobleme mit einem Levi-Civita Zusammenhang. Siegfried Steiner (1986) Mathematische Zeitschrift