Hi Gianmaria,
You are trying to use Scheme as though it were C. It isn't. I'd really like you to read the book I referred you to recently.
If you really must learn about how pointers are used underneath everything in Scheme (and which you do not need to know about for programming, mostly), this text is heavily oriented around explaining that aspect:
Most other text refer to locations, rather than using the terminology of pointers.
There are many predicates in Scheme for testing all the types of equivalences of variables. Worth reading the manual.
I have in the past suggested we have another mailing list for the use of scheme in lilypond, but that did not meet general approval. I still think it's a good idea, as I am a bit reluctant to clod the list with very technical Scheme discussions, which is where this is leading.
Andrew