theorem Th5: :: VSDIFF_1:6

for F, G being Field
for V being VectSp of F
for W being VectSp of G
for f being Function of V,W
for x, h being Element of V holds (cD (f,h)) /. x = (f /. (x + (((2 * (1. F)) ") * h))) - (f /. (x - (((2 * (1. F)) ") * h)))