All notes
Logic

Basics

Induction, Counterexample, Contraposition

contraposition
conversion of a proposition from all A is B to all not-B is not-A.

Conjunction, Disjunction

Ref: wikipedia-disjunction.

Logical disjunction
In logic and mathematics, or is the truth-functional operator of (inclusive) disjunction, also known as alternation; the or of a set of operands is true if and only if one or more of its operands is true.