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For many years two-input NAND, AND, NOR, OR and EX-OR gates have been commercially available as cheap quad TTL integrated circuits (IC's). Ideas on quad programmable two-input gates (three inputs per gate) have been published in the literature but have not reached the commercial stage . However, complicated and expensive arithmetic logic units (ALU's) programmable to perform 16 different functions on two 4-bit arguments have become commercially available. The four sections of ALU's are not individually programmable.