
theorem Th17:
  for H,K be finite Group holds
  card product (<* H, K *>) = card(H)*card(K)
  proof
    let H,K be finite Group;
    card (product (<* the carrier of H,the carrier of K *>))
    = card(the carrier of product (<* H, K *>)) by Th10;
    hence thesis by Th2;
  end;
