Some new research at the University of Ohio in Miami: They have defined two new logic elements that promise to revolutionize the computing industry: BUT and Exclusive AND...The first, the BUT gate, is a natural complement to the classic primitives of AND, OR, and NOT, the most fundamental of logic elements...As with language, the BUT gate serves to negate what was asserted immediately before by the other input. Since there are two inputs to the basic BUT, there must necessarily be two outputs, each negating the other’s prior state according to which input appeared last....To date, efforts to plot this function on a Karnaugh map have been found perplexing.
-- The Chip Insider, VLSI Research, April 1, 2009