reserve n,m for Element of NAT;
reserve h,k,r,r1,r2,x,x0,x1,x2,x3 for Real;
reserve f,f1,f2 for Function of REAL,REAL;

theorem Th16:
  cdif(f,h).1 = cD(f,h)
proof
  cdif(f,h).1 = cdif(f,h).(0+1) .= cD(cdif(f,h).0,h) by DIFF_1:def 8
    .= cD(f,h) by DIFF_1:def 8;
  hence thesis;
end;
