Referencing equations in/from appendix I am currently writing a thesis in which a lot of derivations are moved to the appendix. To make these derivations readable, I sometimes write sentences like "As we saw in equation X...", where equation X is present both in the main text as well as in the appendix. 

My question: should I, while writing the appendix, reference the instance of the equation in the main text, or the one in the appendix?
In general, it is always easier if your cross-reference is relatively nearby—flipping between multiple parts of a text makes the whole thing harder to understand.

So I'd lean towards referencing the version in the appendix, all other things being equal. However, if you are referencing a whole series of equations in the main text, including one duplicated in the Appendix, then it would be OK to preserve the main-text reference.