AudioBOOLEAN ALGEBRA
Boolean (George Boole 1815-1864) algebra considers functions of variables which can assume only two values:
Such values are generally associated with the following symbols:
0 (indicating False value)
In electrical circuits:
a variable may indicate the presence (positive logic)
or the absence (negative logic)of a predetermined tension value.
Usually Boolean variables are identified with letters as: A.
The interaction between variables, determined by logic links (e.g. B is true if A is false ), is expressed by functions of the following type:
Where 
is the negation of A ( i.e. is True if A is false).
Note:
The first application of Boolean algebra was in the railroad field where Boolean variables indicated the position of rail switches.