gates work unpublished first published proof henry sheffer nand logical operation sometimes called sheffer stroke logical sometimes called ''peirce 's arrow'' ref name b ninglettmann ref consequently gates sometimes called ''universal logic gates'' ref name bird ref eventually vacuum tubes replaced relays logic operations lee de forest 's modification fleming valve used logic gate ludwig wittgenstein introduced version row truth table proposition ''tractatus logico philosophicus'' walther bothe inventor coincidence circuit got
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