Tonelli 1915: lower-semicontinuous coercive functional on weakly-closed sequentially-compact set attains minimum. Modern existence-proofs in calculus-of-variations + PDE. Sobolev-space framework. Underlies γ-convergence (De Giorgi 1975).
Tonelli 1915: lower-semicontinuous coercive functional on weakly-closed sequentially-compact set attains minimum. Modern existence-proofs in calculus-of-variations + PDE. Sobolev-space framework. Underlies γ-convergence (De Giorgi 1975).