Here, the variables we are allowed to manipulate can take only two values: True or False. They are Boolean variables. Thus, if x is such a variable, either x has the value True (x = True), or x has the value False (x = False). Elementary and limited though these values may be, we can still perform computations with them. To do so, we define operations, rather like addition or taking reciprocals for ordinary (non-zero) numbers.
Saying no, no, no…
-----------------------
The first operation is negation: if x is a variable with a given Boolean value, then ¬ x has the "opposite" value to x, in the sense that ¬True = False and ¬False = True. The operator ¬ is read as "Not" (so Not(True) = False, which seems logical!).
To define our second operation, we need to simplify the standard formalism slightly. A 3-clause is a triple consisting of variables or negated variables. The variables making up a 3-clause must be distinct, but their order within the triple is immaterial. Here are a few examples of 3-clauses involving the Boolean variables x, y, z and t:
(x, y, t),
