I appreciate your curiosity. In regard to the information you give (that you are a secondary school student, etc.), I'd recommend you (I suspect, as second to none) Douglas Hofstadter's Gödel, Escher, Bach: An Eternal Golden Braid in order to form a firm conceptual basis (which is indispensable not to get lost on the way). Aiming at a popular audience, the discussion roams over a broad range of topics the author intertwines. The following excerpt (p. 94) may suggest that it covers also the subjects you look for:
A full formalization of geometry would take the drastic step of making
every term undefined—that is, turning every term into a "meaningless"
symbol of a formal system. I put quotes around "meaningless" because,
as you know, the symbols automatically pick up passive meanings in
accordance with the theorems they occur in. It is another question,
though, whether people discover those meanings, for to do so requires
finding a set of concepts which can be linked by an isomorphism to the
symbols in the formal system. If one begins with the aim of
formalizing geometry, presumably one has an intended interpretation
for each symbol, so that the passive meanings are built into the
system. That is what I did for p and q when I first created the
pq-system.
But there may be other passive meanings which are potentially
perceptible, which no one has yet noticed. For instance, there were the
surprise interpretations of p as "equals" and q as "taken from", in
the original pq-system. Although this is rather a trivial example, it
contains the essence of the idea that symbols may have many meaningful
interpretations—it is up to the observer to look for them.
We can summarize our observations so far in terms of the word
"consistency".
We began our discussion by manufacturing what appeared to be an
inconsistent formal system—one which was internally inconsistent, as
well as inconsistent with the external world. But a moment later we
took it all back, when we realized our error: that we had chosen
unfortunate interpretations for the symbols. By changing the
interpretations, we regained consistency! It now becomes clear that
consistency is not a property of a formal system per se, but depends on the interpretation which is proposed for it. By the same token,
inconsistency is not an intrinsic property of any formal system.
As for the style of the book, these words from a review give a fair description:
Professor Hofstadter's presentation of these ideas is not rigorous, in
the mathematical sense, but all the essential steps are there; the
reader is not asked to accept results on authority or on faith. Nor is
the narrative rigorous in the uphill-hiking sense, for the author is
always ready to take the reader's hand and lead him through the
thickets.
The book has been translated, published and read all over the world since 1979. You can freely read it at or download its pdf from archive.org. I suppose one can get a second-hand in-good-condition copy of it at quite an affordable price today.
