Leonhardi Euleri Methodus inveniendi lineas curvas : maximi minimive proprietate gaudentes sive solutio problematis isoperimetrici latissimo sensu accepti / edidit Constantin Carathéodory ; Vorwort Andreas Speiser ; auctoritate et impensis Societatis Scientiarum Naturalium Helveticae. - Euler, Leonhard (1707-1783) (Euler, Leonhard (1707-1783). Opera omnia. Opera mathematica, 1952)