I'm writing a mathematical paper, and right now I'm using
to enumerate theorems, propositions, etc. In this way, every statement shows the number of the chapter, the number of the section and then the number of the statement in that section.
This is quite standard, but I would like to do it something differently: I'd like to omit the chapter number when stating the propositions, but show it every time I'm referring to that proposition outside the chapter.
I've already seen it in some books, is there an easy way to do it?