theorem
  Product ((i+j) |->z) = (Product (i|->z))*(Product (j|->z))
proof
  reconsider i,j as Nat by TARSKI:1;
  Product ((i+j) |->z) = multcomplex.(multcomplex$$(i|->z),multcomplex$$(j
  |->z)) by SETWOP_2:26
    .= (Product (i|->z))*(Product (j|->z)) by BINOP_2:def 5;
  hence thesis;
end;
