twovalued logic
<logic> (Commonly known as "Boolean algebra") A mathematical system
concerning the two truth values, TRUE and FALSE and the functions AND, OR, NOT.
Twovalued logic is one of the cornerstones of logic and is also fundamental in
the design of digital electronics and programming languages.
The term "Boolean" is used here with its common meaning  twovalued, though
strictly Boolean algebra is more general than this.
Boolean functions are usually represented by truth tables where "0" represents
"false" and "1" represents "true". E.g.:
A  B  A AND B
++
0  0  0
0  1  0
1  0  0
1  1  1
This can be given more compactly using "x" to mean "don't care" (either
true or false):
A  B  A AND B
++
0  x  0
x  0  0
1  1  1
Similarly:
A  NOT A A  B  A OR B
+ ++
0  1 0  0  0
1  0 x  1  1
1  x  1
Other functions such as XOR, NAND, NOR or functions of more than two
inputs can be constructed using combinations of AND,
OR, and NOT. AND and OR can be constructed from each
other using DeMorgan's Theorem:
A OR B = NOT ((NOT A) AND (NOT B))
A AND B = NOT ((NOT A) OR (NOT B))
In fact any Boolean function can be constructed using just NOR or just
NAND using the identities:
NOT A = A NOR A
A OR B = NOT (A NOR B)
and DeMorgan's Theorem.
(20030618)
Nearby terms:
twophase commit « twos complement « twototheN «
twovalued logic » TX0 » TXL » TYMCOMX
