. . . the contradictory opposite of a copulative proposition is a disjunctive proposition composed of the contradictory opposites of its parts.
. . . the contradictory opposite of a disjunctive proposition is a copulative proposition composed of the contradictories of the parts of the disjunctive proposition.
Summa totius logicae (transl. P Boehner 1955)
[Note: This is Ockham's formulation of De Morgan's Laws.]
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