Editing Mutual exclusivity (section)

==Logic==
{{See also|Logical possibility}}
In [[logic]], two propositions <math> \phi </math> and <math> \psi </math> are mutually exclusive if it is [[logical possibility|not logically possible]] for them to be true at the same time; that is, <math> \lnot (\phi \land \psi) </math> is a tautology. To say that more than two propositions are mutually exclusive, depending on the context, means either 1. "<math> \lnot (\phi_1 \land \phi_2) \and \lnot (\phi_1 \land \phi_3) \and \lnot (\phi_2 \land \phi_3) </math> is a tautology" (it is not logically possible for more than one proposition to be true) or 2. "<math> \lnot (\phi_1 \land \phi_2 \land \phi_3) </math> is a tautology" (it is not logically possible for all propositions to be true at the same time). The term ''pairwise mutually exclusive'' always means the former.