Double Input–Double Output Systems
Some molecular logic systems with double inputs and double outputs serve important arithmetic functions. These are the half-adders and half-subtractors, including bidirectional versions where appropriate. Molecular number processing begins here. Magnitude comparators are also featured. Although the 1:2 demultiplexer is briefly mentioned, it is held back for proper discussion with its counterpart 2:1 multiplexer in Chapter 10. Some reversible logic aspects of bidirectional half-subtractors are also noted.