theorem
  for g1 be PartFunc of REAL n,REAL 1 holds g1 = <>*g implies (g1
  is_partial_differentiable_in y,i iff g is_partial_differentiable_in y,i)
proof
  let g1 be PartFunc of REAL n,REAL 1;
  assume
A1: g1=<>*g;
  reconsider y9=y as Point of REAL-NS n by REAL_NS1:def 4;
  the carrier of REAL-NS 1 = REAL 1 by REAL_NS1:def 4;
  then reconsider h=g1 as PartFunc of REAL-NS n,REAL-NS 1 by REAL_NS1:def 4;
  h is_partial_differentiable_in y9,i iff g1 is_partial_differentiable_in
  y, i;
  hence thesis by A1,Th14;
end;
