let h, x be Real; for f being Function of REAL,REAL holds [!f,(x - h),x!] = (((bdif (f,h)) . 1) . x) / h
let f be Function of REAL,REAL; [!f,(x - h),x!] = (((bdif (f,h)) . 1) . x) / h
[!f,(x - h),x!] =
[!f,x,(x - h)!]
by DIFF_1:29
.=
((bD (f,h)) . x) / h
by DIFF_1:4
.=
((bD (((bdif (f,h)) . 0),h)) . x) / h
by DIFF_1:def 7
.=
(((bdif (f,h)) . (0 + 1)) . x) / h
by DIFF_1:def 7
;
hence
[!f,(x - h),x!] = (((bdif (f,h)) . 1) . x) / h
; verum