Niels Henrik Abel partially proves that the general quintic or higher equations cannot be solved by a general formula involving only arithmetical operations and roots.
Augustin Louis Cauchy proves convergence of the Euler method. In this proof, Cauchy uses the implicit Euler method
"Every normal man must be tempted at times to spit upon his hands, hoist the
black flag, and begin slitting throats."
- Henry Louis Mencken (1880-1956)
