Sentence:  I particularly remember how, at that time, I was using his <WSD>mollifier</WSD> method to study the zero density of L-functions and was stuck with something. 
Meaning of the word marked with <WSD> tags:  An "approximation to the identity", a smooth function with special properties, used in distribution theory to create sequences of smooth functions approximating nonsmooth (generalized) functions, via convolution.