reserve S,T for RealNormSpace;
reserve f,f1,f2 for PartFunc of S,T;
reserve Z for Subset of S;
reserve i,n for Nat;

theorem
for n be Nat, f be PartFunc of S,T st 1<= n & f is_differentiable_on n,Z
 holds -f is_differentiable_on n,Z
proof
   let n be Nat, f be PartFunc of S,T;
   assume 1 <= n & f is_differentiable_on n, Z; then
   (-1)(#)f is_differentiable_on n,Z by Th25;
   hence thesis by VFUNCT_1:23;
end;
