Definition of a differentiable function

[Dragonfall]

I need to know the definition of a differentiable function at a point in Banach spaces, my notes has a certain ambiguity and I can't find a book with the definition. Thanks.

 

[quasar987]

have you cheked wiki?

http://en.wikipedia.org/wiki/Banach_space#Derivatives

 

[Dragonfall]

The wiki ones do not correspond (though I'm sure they are equivalent) to what we use. I found my definition from some obscure source, but thanks anyway.