theorem
  Product ((i*j) |->r) = Product (j |-> (Product (i|->r)))
proof
  reconsider r as Element of REAL by XREAL_0:def 1;
  reconsider pr = Product (i|->r) as Element of REAL;
  i is Nat & j is Nat by TARSKI:1;
  then Product ((i*j) |->r) = Product (j |-> pr) by SETWOP_2:27;
  hence thesis;
end;
