Sentence:  If * * f denotes the space of n times continuously differentiable <WSD>functions</WSD> , then the space V of solutions of this differential equation is a subspace of * * f . 
Meaning of the word marked with <WSD> tags:  (mathematics) a mathematical relation such that each element of a given set (the domain of the function) is associated with an element of another set (the range of the function)