Page "Discrete mathematics" Paragraph 17

Logical formulas are discrete structures, as are proofs, which form finite trees or, more generally, directed acyclic graph structures ( with each inference step combining one or more premise branches to give a single conclusion ).

The truth values of logical formulas usually form a finite set, generally restricted to two values: true and false, but logic can also be continuous-valued, e. g., fuzzy logic.

Concepts such as infinite proof trees or infinite derivation trees have also been studied, e. g. infinitary logic.