Sheffer's stroke

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Charles Sanders Peirce (1839—1914) American philosopher and logician



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Both Peirce in 1880 and the American logician H. M. Sheffer in 1913 realized that the truth-functions of elementary logic could all be defined from a single function. Defining p / q to mean not both p and q, p / p is equivalent to not-p, (p / q)/ (p / q) means pq, and so on. The sign for this truth-function is Sheffer's stroke: p / q is true only when p is false or q is false. A functionally complete system can also be built from a single sign for the function that is true when p is false and q is false.

Subjects: Philosophy.

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