reserve E for non empty set;
reserve a for Element of E;
reserve A, B for Subset of E;
reserve Y for set;
reserve p for FinSequence;
reserve e, e1, e2 for Singleton of E;

theorem Th18:
  for E being finite non empty set, A being Event of E holds 0 <= prob(A)
proof
  let E be finite non empty set, A be Event of E;
  0 < card E & 0 <= card A by Lm1,CARD_1:27;
  hence thesis;
end;
