Sheffer stroke

Summary

In Boolean functions and propositional calculus, the Sheffer stroke denotes a logical operation that is equivalent to the negation of the conjunction operation, expressed in ordinary language as "not both". It is also called non-conjunction, alternative denial (since it says in effect that at least one of its operands is false), or NAND ("not and"). In digital electronics, it corresponds to the NAND gate. It is named after Henry Maurice Sheffer and written as $\mid$ or as $\uparrow$ or as $\overline{\wedge}$ or as $Dpq$ in Polish notation by Łukasiewicz (but not as ||, often used to represent disjunction).