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Triple Negative (Posted on 2004-02-12) Difficulty: 4 of 5
Using only two inverters and an unlimited number of AND and OR gates in a logic circuit, show how to invert an arbitrary number of inputs.

(For instance, if you have four inputs, the circuit will have four outputs that are the inverses of the four inputs)

No Solution Yet Submitted by DJ    
Rating: 4.1250 (8 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: So... | Comment 15 of 19 |
(In reply to So... by Charlie)

It seems unlikely to me that DJ would make such a major mistake in his problem statement. There are many unintuitive things in Boolean algebra such as the "Sheffer stroke" (c. f. http://www.swif.uniba.it/lei/foldop/foldoc.cgi?Sheffer+stroke), which is the "not both" Boolean function (better known to circuit designers as "NAND") in terms of which every other Boolean function, including negation, can be expressed ("neither/nor" aka "dagger" aka "NOR" has the same property). What is needed is to clearly see why the known method works for 3 inputs--maybe then we will be able to see why it can or cannot be generalized to work for n inputs.
Edited on February 16, 2004, 10:00 pm
  Posted by Richard on 2004-02-14 23:48:49

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