Sentence:  What is amazing is that "a concept that is created by mind itself, the sequence of integers, the simplest and most <WSD>diaphanous</WSD> thing for the constructive mind, assumes a similar aspect of obscurity and deficiency when viewed from the axiomatic angle" (Weyl, 1963, 220). 
Meaning of the word marked with <WSD> tags:  Of a fine, almost transparent, texture; gossamer; light and insubstantial.