let h, x be Real; :: thesis: for f being Function of REAL,REAL holds [!f,(x - h),x!] = ((bD (f,h)) . x) / h
let f be Function of REAL,REAL; :: thesis: [!f,(x - h),x!] = ((bD (f,h)) . x) / h
[!f,(x - h),x!] = (((bdif (f,h)) . 1) . x) / h by DIFF_2:3
.= ((bD (f,h)) . x) / h by Th11 ;
hence [!f,(x - h),x!] = ((bD (f,h)) . x) / h ; :: thesis: verum