COMPUTABILITY THEORY
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The area of theoretical computer scienceconcerning what problems can be solved by any computer.A function is computable if an algorithm can be implementedwhich will give the correct output for any valid input.Since computer programs are countable but real numbers arenot, it follows that there must exist real numbers thatcannot be calculated by any program. Unfortunately, bydefinition, there isn't an easy way of describing any of them!In fact, there are many tasks (not just calculating realnumbers) that computers cannot perform. The most wellknownis the halting problem, the busy beaver problem is lessfamous but just as fascinating.["Computability", N.J. Cutland. (A well writtenundergraduatelevel introduction to the subject)].["The Turing Omnibus", A.K. Dewdeney].
By Denis Howe
Word of the day
Epithelioid Leiomyoma
 A relatively rare smooth muscle tumor found most frequently in the wall gastrointestinal tract, especially stomach. It similar to other tumors but may become very large and hemorrhage exhibit small cystic areas. Simple excision is almost always curative. (From Dorland, 27th ed; DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, p1354)