let h be Real; :: thesis: for f being Function of REAL ,REAL
for n being Nat holds (cdif f,h) . n is Function of REAL ,REAL
let f be Function of REAL ,REAL ; :: thesis: for n being Nat holds (cdif f,h) . n is Function of REAL ,REAL
defpred S₁[ Nat] means (cdif f,h) . $1 is Function of REAL ,REAL ;
A1: for k being Nat st S₁[k] holds
S₁[k + 1]

proof

let k be Nat; :: thesis: ( S₁[k] implies S₁[k + 1] )
assume (cdif f,h) . k is Function of REAL ,REAL ; :: thesis: S₁[k + 1]
then cD ((cdif f,h) . k),h is Function of REAL ,REAL by Lm3;
hence S₁[k + 1] by Def8; :: thesis: verum

end;

A2: S₁[ 0 ] by Def8;
for n being Nat holds S₁[n] from NAT_1:sch 2(A2, A1);
hence for n being Nat holds (cdif f,h) . n is Function of REAL ,REAL ; :: thesis: verum