 reserve n,m,i,p for Nat,
         h,k,r,r1,r2,x,x0,x1,x2,x3 for Real;
 reserve f,f1,f2,g for Function of REAL,REAL;

theorem
  bD(f,h).x = f.x - Shift(f,-h).x
proof
  bD(f,h).x = (bdif(f,h).1).x by DIFF_3:11
    .= f.x - Shift(f,-h).x by DIFF_1:18;
  hence thesis;
end;
