This represents the weakest precondition of a command S with respect to a postcondition R . The building blocks for logical constructs are the set of all declarative sentences. The only declarative sentences of interest are those that can be classified as true or false , but not both. Propositions may be elementary or compound sentences. Compound sentences can be built from elementary propositions that are joined or modified using a set of well-defined connectives or operators.
Connectives Let p and q be statements.
It is called the conjunction of p and q . It is called the disjunction of p and q . The Exclusive OR of p and q , denoted by , is the proposition that is true when exactly one of p and q is true and false otherwise. The only time an implication is not true is when a true statement implies a false one. Examples is true . is false .