In logic, Nicod's axiom (named after the French logician and philosopher Jean Nicod) is a formula that can be used as the sole axiom of a semantically complete system of propositional calculus. The only connective used in the formulation of Nicod's axiom is the Sheffer's stroke.
The axiom has the following form:
Nicod showed that the whole propositional logic of Principia Mathematica could be derived from this axiom alone by using one rule of inference, called "Nicod's modus ponens":
In 1931, the Polish logician Mordechaj Wajsberg discovered an equally powerful and easier-to-work-with alternative: