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

theorem Th2:
  {} is OrthogonalFamily of X
proof
A1: {} is Subset of X by SUBSET_1:1;
  x in {} & y in {} & x <> y implies x.|.y = 0;
  hence thesis by A1,Def8;
end;
