theorem
  for E being finite non empty set, A,B being Event of E st 0 < prob(B)
  & A, B are_independent holds prob(A, B) = prob(A)
proof
  let E be finite non empty set, A,B be Event of E;
  assume that
A1: 0 < prob(B) and
A2: A, B are_independent;
  prob(A /\ B) = prob(A) * prob(B) by A2;
  then prob(A, B) = prob(A) * ( prob(B) / prob(B) ) by XCMPLX_1:74;
  then prob(A, B) = prob(A) * 1 by A1,XCMPLX_1:60;
  hence thesis;
end;
