 reserve G, A for Group;
 reserve phi for Homomorphism of A,AutGroup(G);
 reserve G, A for Group;
 reserve phi for Homomorphism of A,AutGroup(G);
reserve G1,G2 for Group;

theorem :: TH97
  for n being non zero Nat
  holds card (Dihedral_group n) = 2*n
proof
  let n be non zero Nat;
  thus card (Dihedral_group n) = (card (INT.Group n))*(card (INT.Group 2))
    by Th74
                              .= 2*n;
end;
