Events and axioms

An event is a subset of a sample space. Its complement contains outcomes outside it; the union A∪B means A or B inclusive; intersection A∩B means both. Probabilities are nonnegative, P(S)=1 and probabilities add over disjoint events. For equally likely outcomes only, P(A)=number of favourable outcomes/number of outcomes. A probability of zero need not mean a logically impossible event in a continuous model.