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In page Sheffer stroke:

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In 1913, Sheffer described non-disjunction using {\displaystyle \mid } and showed its functional completeness. Sheffer also used {\displaystyle \wedge } for non-disjunction.[citation needed] Many people, beginning with Nicod in 1917, and followed by Whitehead, Russell and many others, mistakenly thought Sheffer has described non-conjunction using {\displaystyle \mid } , naming this the Sheffer stroke.