reserve X1,X2,X3,X4 for set;
reserve n for non zero Nat;
reserve X for non-empty n-element FinSequence;

theorem Thm28:
  for X being non-empty 1-element FinSequence, S being SemiringFamily of X
  holds SemiringProduct(S) is semiring_of_sets of product X
  proof
    let X be non-empty 1-element FinSequence, S be SemiringFamily of X;
    set S1=the set of all product <*s*> where s is Element of S.1;
    set X1=the set of all <*x*> where x is Element of X.1;
    S1 = SemiringProduct(S) & X1 = product X by Thm21,Thm24;
    hence thesis by Thm27;
  end;
