Formal logic, or, The calculus of inference, necessary and probable
Augustus De Morgan · Zenodo (CERN European Organization for Nuclear Research) · 2002
Augustus De Morgan (1806 – 1871), a British mathematician and logician, introduced the term mathematical induction and formulated De Morgan's laws. More or less, De Morgan's theorem was already known by William of Ockham in the 14th century (see William of Ockham, Summa Logicae, part II, sections 32 and 33). Following De Morgan, a negation of a disjunction is the conjunction of the negations. Furthermore, a negation of a conjunction is the disjunction of the negations (see Book, p. 118). In simple words: not (A or B) = (not A) and (not B). Equally, it is true that not (A and B) = (not A) or (not B). Download at: Archive