Augustus De Morgan was an Indian-born British mathematician and logician. He was born in 1806 and died in 1871. He proved an important result that set intersection and set union were dual under complementation.
- ie: complement( S intersect T ) == complement(S) union complement(T)
- and complement( S union T ) == complement(S) intersect complement(T)
Charles Peirce showed that this result appled to logical and for intersect, logical or for union, and logical negation for complement.