  In Boolean algebra, it is known that the logical function that corresponds to
the negation of the conjunction --NAND-- is universal in the sense that any
other logical function can be built based on it. This property makes it
essential to modern digital electronics and computer processor design. Here, we
design a molecular Turing machine that computes the NAND function over binary
strings of arbitrary length. For this purpose, we will perform a mathematical
abstraction of the kind of operations that can be done over a double-stranded
DNA molecule, as well as presenting a molecular encoding of the input symbols
for such a machine.
