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
  for E being finite non empty set, A being Event of E holds prob(A, A`) = 0
proof
  let E be finite non empty set, A be Event of E;
  A misses A` by SUBSET_1:24;
  then prob(A /\ A`) = 0 by Th16;
  hence thesis;
end;
