Unless there is a reason to diverge, we follow the conventions of
the Metamath Proof Explorer (aka "set.mm"). This list of
conventions is intended to be read in conjunction with the
corresponding conventions in the Metamath Proof Explorer, and
only the differences are described below.
- Minimizing axioms and the axiom of choice.
We prefer proofs that depend on fewer and/or weaker axioms,
even if the proofs are longer. In particular, our choice of IZF
(Intuitionistic Zermelo-Fraenkel) over CZF (Constructive
Zermelo-Fraenkel, a weaker system) was just an expedient choice
because IZF is easier to formalize in metamath. You can find some
development using CZF in BJ's mathbox starting at ax-bd0 9933 (and the
section header just above it).
As for the axiom of choice, the full axiom of choice implies
excluded middle as seen at acexmid 5511, although some authors will
use countable choice or dependent choice. For example, countable
choice or excluded middle is needed to show that the Cauchy reals
coincide with the Dedekind reals - Corollary 11.4.3 of [HoTT],
- Junk/undefined results.
Much of the discussion of this topic in the Metamath Proof
Explorer applies except that certain techniques are not
available to us. For example, the Metamath Proof Explorer will
often say "if a function is evaluated within its domain, a
certain result follows; if the function is evaluated outside
its domain, the same result follows. Since the function must
be evaluated within its domain or outside it, the result follows
unconditionally" (the use of excluded middle in this argument is
perhaps obvious when stated this way). For this reason, we
generally need to prove we are evaluating functions within
their domains and avoid the reverse closure theorems of the
Metamath Proof Explorer.
- Bibliography references.
The bibliography for the Intuitionistic Logic Explorer is
separate from the one for the Metamath Proof Explorer but feel
free to copy-paste a citation in either direction in order to
Label naming conventions
Here are a few of the label naming conventions:
We follow the conventions of the Metamath Proof Explorer with a few
additions. A biconditional in set.mm which is an implication in
iset.mm should have a "r" (for the reverse direction), or "i"/"im"
(for the forward direction) appended. A theorem in set.mm which has
a decidability condition added should add "dc" to the theorem name.
A theorem in set.mm where "nonempty class" is changed to "inhabited
class" should add "m" (for member) to the theorem name.
The following table shows some commonly-used abbreviations in labels
which are not found in the Metamath Proof Explorer,
in alphabetical order.
For each abbreviation we provide a mnenomic to help you remember it,
the source theorem/assumption defining it, an expression showing
what it looks like, whether or not it is a "syntax fragment"
(an abbreviation that indicates a particular kind of syntax), and
hyperlinks to label examples that use the abbreviation.
The abbreviation is bolded if there is a df-NAME definition but
the label fragment is not NAME.
|ap||apart|| df-ap 7573
|| ||Yes|| apadd1 7599, apne 7614 |
The Metamath mailing list also covers the Intuitionistic Logic
Explorer and is at:
(Contributed by Jim Kingdon, 24-Feb-2020.)