Sentence:  If a function is continuous then its <WSD>kernel</WSD> is a closed se 
Meaning of the word marked with <WSD> tags:  For a given function (especially a linear map between vector spaces), the set of elements in the domain which are mapped to zero;  given "f" : "X" → "Y", the set {"x" ∈ "X" : "f"("x") = 0}.