theorem :: NDIFF_1:41

for S, T being RealNormSpace
for Z being Subset of S st Z is open holds
for r being Real
for f being PartFunc of S,T st Z c= dom (r (#) f) & f is_differentiable_on Z holds
( r (#) f is_differentiable_on Z & ( for x being Point of S st x in Z holds
((r (#) f) `| Z) /. x = r * (diff (f,x)) ) )