reserve X for RealUnitarySpace;
reserve x, y, y1, y2 for Point of X;
reserve xd for set;
reserve i, j, n for Nat;

theorem Th3:
  {} is OrthonormalFamily of X
proof
A1: {} is OrthogonalFamily of X by Th2;
  x in {} implies x.|.x = 1;
  hence thesis by A1,Def9;
end;
