The axiom of bivalence of truth motivates a formal definition of the values true and false as elements of a set. This set of truth values will be just a convenient notation used frequently later on in the text.
The set of truth values contains the elements \[\mathbb B:=\{\text{false},\text{true}\}:=\{0,1\}=\{\text{no},\text{yes}\}.\]
Definitions: 1 2 3 4
Examples: 5
Lemmas: 6 7
Proofs: 8 9 10 11