It is well known that the theory of reflections was considerably developed during the 19th century with the development of group theory (e.g. Klein) and the theory of transformations. However, I'm interested to know who were the mathematicians that dealt with reflections during the 18th century and the beginning of the 19th century. A colleague of mine mentioned that several mathematicians looked on reflections in terms of foldings, in order to see if curves intersect themselves while being reflected; However, I didn't manage to find any sources for that.
Hence, any reference would be appreciated!
