Boolean Algebra

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

Background

The branch of algebra in which the values of the variables are the truth values true and false, usually denoted 1 and 0 respectively. It is a formal description of logical relations. It was introduced by George Boole in his first book The Mathematical Analysis of Logic in 1847.

Logic Gates

An idealized or physical device implementing a Boolean function; that is, it performs a logical operation on one or more binary inputs and produces a single binary output.

Formal Name	Abbreviated Name	Symbol	Gate	Truth Table
Buffer				Inputs Outputs $A$ $Q=A$ 0 0 1 1
Conjunction	AND	$A\land B$		Inputs Outputs $A$ $B$ $Q=A\land B$ 0 0 0 0 1 0 1 0 0 1 1 1
Disjunction	OR	$A\lor B$		Inputs Outputs $A$ $B$ $Q=A\lor B$ 0 0 0 0 1 1 1 0 1 1 1 1
Exclusive OR	XOR	$A\oplus B$		Inputs Outputs $A$ $B$ $Q=A\oplus B$ 0 0 0 0 1 1 1 0 1 1 1 0
Inverter	NOT	$\neg A$		Inputs Outputs $A$ $Q={\overline {A}}$ 0 1 1 0
Negated Conjunction	NAND	${\overline {A\land B}}$		Inputs Outputs $A$ $B$ $Q={\overline {A\land B}}$ 0 0 1 0 1 1 1 0 1 1 1 0
Negated Disjunction	NOR	${\overline {A\lor B}}$		Inputs Outputs $A$ $B$ $Q={\overline {A\lor B}}$ 0 0 1 0 1 0 1 0 0 1 1 0
Negated Exclusive OR	NOT XOR	${\overline {A\oplus B}}$		Inputs Outputs $A$ $B$ $Q={\overline {A\oplus B}}$ 0 0 1 0 1 0 1 0 0 1 1 1

Composition

Logic gates can be cascaded in the same way that Boolean functions can be composed, allowing the construction of a physical model of all of Boolean logic.

De Morgan's Laws

• $A\land B\Leftrightarrow \neg (\neg X\lor \neg Y)$
• $A\lor B\Leftrightarrow \neg (\neg X\land \neg Y)$

References

• Boolean Algebra (Wikipedia)
• De Morgan's Laws (Wikipedia)
• Logic Gates (Wikipedia)