reserve a,b for object, I,J for set;
reserve b for bag of I;

theorem Th25:
  for p being Bags I-valued FinSequence holds Sum (<*b*>^p) = b + Sum p
  proof
    let p be Bags I-valued FinSequence;
    thus Sum (<*b*>^p) = Sum <*b*> + Sum p by Th24
    .= b + Sum p by Th23;
  end;
