Smullyan 1968, p. 14: "Make a truth-table for the formula. Each line of the table which comes out "T" will yield one of the basic conjunctions of the disjunctive normal form." Smullyan, Raymond M. (1968). First-Order Logic. Ergebnisse der Mathematik und ihrer Grenzgebiete. Vol. 43 (1st edition, Second Printing 1971 ed.). New York Heidelberg Berlin: Springer-Verlag. p. 160. doi:10.1007/978-3-642-86718-7. ISBN978-3-642-86718-7.