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Type | Label | Description |
---|---|---|
Statement | ||
Theorem | nnsf 14201* | Domain and range of . Part of Definition 3.3 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 30-Jul-2022.) |
ℕ∞ ℕ∞ℕ∞ | ||
Theorem | peano4nninf 14202* | The successor function on ℕ∞ is one to one. Half of Lemma 3.4 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 31-Jul-2022.) |
ℕ∞ ℕ∞ℕ∞ | ||
Theorem | peano3nninf 14203* | The successor function on ℕ∞ is never zero. Half of Lemma 3.4 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 1-Aug-2022.) |
ℕ∞ ℕ∞ | ||
Theorem | nninfalllem1 14204* | Lemma for nninfall 14205. (Contributed by Jim Kingdon, 1-Aug-2022.) |
ℕ∞ ℕ∞ | ||
Theorem | nninfall 14205* | Given a decidable predicate on ℕ∞, showing it holds for natural numbers and the point at infinity suffices to show it holds everywhere. The sense in which is a decidable predicate is that it assigns a value of either or (which can be thought of as false and true) to every element of ℕ∞. Lemma 3.5 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 1-Aug-2022.) |
ℕ∞ ℕ∞ | ||
Theorem | nninfsellemdc 14206* | Lemma for nninfself 14209. Showing that the selection function is well defined. (Contributed by Jim Kingdon, 8-Aug-2022.) |
ℕ∞ DECID | ||
Theorem | nninfsellemcl 14207* | Lemma for nninfself 14209. (Contributed by Jim Kingdon, 8-Aug-2022.) |
ℕ∞ | ||
Theorem | nninfsellemsuc 14208* | Lemma for nninfself 14209. (Contributed by Jim Kingdon, 6-Aug-2022.) |
ℕ∞ | ||
Theorem | nninfself 14209* | Domain and range of the selection function for ℕ∞. (Contributed by Jim Kingdon, 6-Aug-2022.) |
ℕ∞ ℕ∞ℕ∞ | ||
Theorem | nninfsellemeq 14210* | Lemma for nninfsel 14213. (Contributed by Jim Kingdon, 9-Aug-2022.) |
ℕ∞ ℕ∞ | ||
Theorem | nninfsellemqall 14211* | Lemma for nninfsel 14213. (Contributed by Jim Kingdon, 9-Aug-2022.) |
ℕ∞ ℕ∞ | ||
Theorem | nninfsellemeqinf 14212* | Lemma for nninfsel 14213. (Contributed by Jim Kingdon, 9-Aug-2022.) |
ℕ∞ ℕ∞ | ||
Theorem | nninfsel 14213* | is a selection function for ℕ∞. Theorem 3.6 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 9-Aug-2022.) |
ℕ∞ ℕ∞ ℕ∞ | ||
Theorem | nninfomnilem 14214* | Lemma for nninfomni 14215. (Contributed by Jim Kingdon, 10-Aug-2022.) |
ℕ∞ ℕ∞ Omni | ||
Theorem | nninfomni 14215 | ℕ∞ is omniscient. Corollary 3.7 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 10-Aug-2022.) |
ℕ∞ Omni | ||
Theorem | nninffeq 14216* | Equality of two functions on ℕ∞ which agree at every integer and at the point at infinity. From an online post by Martin Escardo. Remark: the last two hypotheses can be grouped into one, . (Contributed by Jim Kingdon, 4-Aug-2023.) |
ℕ∞ ℕ∞ | ||
Theorem | exmidsbthrlem 14217* | Lemma for exmidsbthr 14218. (Contributed by Jim Kingdon, 11-Aug-2022.) |
ℕ∞ EXMID | ||
Theorem | exmidsbthr 14218* | The Schroeder-Bernstein Theorem implies excluded middle. Theorem 1 of [PradicBrown2022], p. 1. (Contributed by Jim Kingdon, 11-Aug-2022.) |
EXMID | ||
Theorem | exmidsbth 14219* |
The Schroeder-Bernstein Theorem is equivalent to excluded middle. This
is Metamath 100 proof #25. The forward direction (isbth 6953) is the
proof of the Schroeder-Bernstein Theorem from the Metamath Proof
Explorer database (in which excluded middle holds), but adapted to use
EXMID as an antecedent rather than being unconditionally
true, as in
the non-intuitionistic proof at
https://us.metamath.org/mpeuni/sbth.html 6953.
The reverse direction (exmidsbthr 14218) is the one which establishes that Schroeder-Bernstein implies excluded middle. This resolves the question of whether we will be able to prove Schroeder-Bernstein from our axioms in the negative. (Contributed by Jim Kingdon, 13-Aug-2022.) |
EXMID | ||
Theorem | sbthomlem 14220 | Lemma for sbthom 14221. (Contributed by Mario Carneiro and Jim Kingdon, 13-Jul-2023.) |
Omni ⊔ | ||
Theorem | sbthom 14221 | Schroeder-Bernstein is not possible even for . We know by exmidsbth 14219 that full Schroeder-Bernstein will not be provable but what about the case where one of the sets is ? That case plus the Limited Principle of Omniscience (LPO) implies excluded middle, so we will not be able to prove it. (Contributed by Mario Carneiro and Jim Kingdon, 10-Jul-2023.) |
Omni EXMID | ||
Theorem | qdencn 14222* | The set of complex numbers whose real and imaginary parts are rational is dense in the complex plane. This is a two dimensional analogue to qdenre 11175 (and also would hold for with the usual metric; this is not about complex numbers in particular). (Contributed by Jim Kingdon, 18-Oct-2021.) |
Theorem | refeq 14223* | Equality of two real functions which agree at negative numbers, positive numbers, and zero. This holds even without real trichotomy. From an online post by Martin Escardo. (Contributed by Jim Kingdon, 9-Jul-2023.) |
Theorem | triap 14224 | Two ways of stating real number trichotomy. (Contributed by Jim Kingdon, 23-Aug-2023.) |
DECID # | ||
Theorem | isomninnlem 14225* | Lemma for isomninn 14226. The result, with a hypothesis to provide a convenient notation. (Contributed by Jim Kingdon, 30-Aug-2023.) |
frec Omni | ||
Theorem | isomninn 14226* | Omniscience stated in terms of natural numbers. Similar to isomnimap 7122 but it will sometimes be more convenient to use and rather than and . (Contributed by Jim Kingdon, 30-Aug-2023.) |
Omni | ||
Theorem | cvgcmp2nlemabs 14227* | Lemma for cvgcmp2n 14228. The partial sums get closer to each other as we go further out. The proof proceeds by rewriting as the sum of and a term which gets smaller as gets large. (Contributed by Jim Kingdon, 25-Aug-2023.) |
Theorem | cvgcmp2n 14228* | A comparison test for convergence of a real infinite series. (Contributed by Jim Kingdon, 25-Aug-2023.) |
Theorem | iooref1o 14229 | A one-to-one mapping from the real numbers onto the open unit interval. (Contributed by Jim Kingdon, 27-Jun-2024.) |
Theorem | iooreen 14230 | An open interval is equinumerous to the real numbers. (Contributed by Jim Kingdon, 27-Jun-2024.) |
Omniscience principles refer to several propositions, most of them weaker than full excluded middle, which do not follow from the axioms of IZF set theory. They are: (0) the Principle of Omniscience (PO), which is another name for excluded middle (see exmidomni 7127), (1) the Limited Principle of Omniscience (LPO) is Omni (see df-omni 7120), (2) the Weak Limited Principle of Omniscience (WLPO) is WOmni (see df-womni 7149), (3) Markov's Principle (MP) is Markov (see df-markov 7137), (4) the Lesser Limited Principle of Omniscience (LLPO) is not yet defined in iset.mm. They also have analytic counterparts each of which follows from the corresponding omniscience principle: (1) Analytic LPO is real number trichotomy, (see trilpo 14238), (2) Analytic WLPO is decidability of real number equality, DECID (see redcwlpo 14250), (3) Analytic MP is # (see neapmkv 14262), (4) Analytic LLPO is real number dichotomy, (most relevant current theorem is maxclpr 11195). | ||
Theorem | trilpolemclim 14231* | Lemma for trilpo 14238. Convergence of the series. (Contributed by Jim Kingdon, 24-Aug-2023.) |
Theorem | trilpolemcl 14232* | Lemma for trilpo 14238. The sum exists. (Contributed by Jim Kingdon, 23-Aug-2023.) |
Theorem | trilpolemisumle 14233* | Lemma for trilpo 14238. An upper bound for the sum of the digits beyond a certain point. (Contributed by Jim Kingdon, 28-Aug-2023.) |
Theorem | trilpolemgt1 14234* | Lemma for trilpo 14238. The case. (Contributed by Jim Kingdon, 23-Aug-2023.) |
Theorem | trilpolemeq1 14235* | Lemma for trilpo 14238. The case. This is proved by noting that if any is zero, then the infinite sum is less than one based on the term which is zero. We are using the fact that the sequence is decidable (in the sense that each element is either zero or one). (Contributed by Jim Kingdon, 23-Aug-2023.) |
Theorem | trilpolemlt1 14236* | Lemma for trilpo 14238. The case. We can use the distance between and one (that is, ) to find a position in the sequence where terms after that point will not add up to as much as . By finomni 7125 we know the terms up to either contain a zero or are all one. But if they are all one that contradicts the way we constructed , so we know that the sequence contains a zero. (Contributed by Jim Kingdon, 23-Aug-2023.) |
Theorem | trilpolemres 14237* | Lemma for trilpo 14238. The result. (Contributed by Jim Kingdon, 23-Aug-2023.) |
Theorem | trilpo 14238* |
Real number trichotomy implies the Limited Principle of Omniscience
(LPO). We expect that we'd need some form of countable choice to prove
the converse.
Here's the outline of the proof. Given an infinite sequence F of zeroes and ones, we need to show the sequence contains a zero or it is all ones. Construct a real number A whose representation in base two consists of a zero, a decimal point, and then the numbers of the sequence. Compare it with one using trichotomy. The three cases from trichotomy are trilpolemlt1 14236 (which means the sequence contains a zero), trilpolemeq1 14235 (which means the sequence is all ones), and trilpolemgt1 14234 (which is not possible). Equivalent ways to state real number trichotomy (sometimes called "analytic LPO") include decidability of real number apartness (see triap 14224) or that the real numbers are a discrete field (see trirec0 14239). LPO is known to not be provable in IZF (and most constructive foundations), so this theorem establishes that we will be unable to prove an analogue to qtri3or 10208 for real numbers. (Contributed by Jim Kingdon, 23-Aug-2023.) |
Omni | ||
Theorem | trirec0 14239* |
Every real number having a reciprocal or equaling zero is equivalent to
real number trichotomy.
This is the key part of the definition of what is known as a discrete field, so "the real numbers are a discrete field" can be taken as an equivalent way to state real trichotomy (see further discussion at trilpo 14238). (Contributed by Jim Kingdon, 10-Jun-2024.) |
Theorem | trirec0xor 14240* |
Version of trirec0 14239 with exclusive-or.
The definition of a discrete field is sometimes stated in terms of exclusive-or but as proved here, this is equivalent to inclusive-or because the two disjuncts cannot be simultaneously true. (Contributed by Jim Kingdon, 10-Jun-2024.) |
Theorem | apdifflemf 14241 | Lemma for apdiff 14243. Being apart from the point halfway between and suffices for to be a different distance from and from . (Contributed by Jim Kingdon, 18-May-2024.) |
# # | ||
Theorem | apdifflemr 14242 | Lemma for apdiff 14243. (Contributed by Jim Kingdon, 19-May-2024.) |
# # # | ||
Theorem | apdiff 14243* | The irrationals (reals apart from any rational) are exactly those reals that are a different distance from every rational. (Contributed by Jim Kingdon, 17-May-2024.) |
# # | ||
Theorem | iswomninnlem 14244* | Lemma for iswomnimap 7151. The result, with a hypothesis for convenience. (Contributed by Jim Kingdon, 20-Jun-2024.) |
frec WOmni DECID | ||
Theorem | iswomninn 14245* | Weak omniscience stated in terms of natural numbers. Similar to iswomnimap 7151 but it will sometimes be more convenient to use and rather than and . (Contributed by Jim Kingdon, 20-Jun-2024.) |
WOmni DECID | ||
Theorem | iswomni0 14246* | Weak omniscience stated in terms of equality with . Like iswomninn 14245 but with zero in place of one. (Contributed by Jim Kingdon, 24-Jul-2024.) |
WOmni DECID | ||
Theorem | ismkvnnlem 14247* | Lemma for ismkvnn 14248. The result, with a hypothesis to give a name to an expression for convenience. (Contributed by Jim Kingdon, 25-Jun-2024.) |
frec Markov | ||
Theorem | ismkvnn 14248* | The predicate of being Markov stated in terms of set exponentiation. (Contributed by Jim Kingdon, 25-Jun-2024.) |
Markov | ||
Theorem | redcwlpolemeq1 14249* | Lemma for redcwlpo 14250. A biconditionalized version of trilpolemeq1 14235. (Contributed by Jim Kingdon, 21-Jun-2024.) |
Theorem | redcwlpo 14250* |
Decidability of real number equality implies the Weak Limited Principle
of Omniscience (WLPO). We expect that we'd need some form of countable
choice to prove the converse.
Here's the outline of the proof. Given an infinite sequence F of zeroes and ones, we need to show the sequence is all ones or it is not. Construct a real number A whose representation in base two consists of a zero, a decimal point, and then the numbers of the sequence. This real number will equal one if and only if the sequence is all ones (redcwlpolemeq1 14249). Therefore decidability of real number equality would imply decidability of whether the sequence is all ones. Because of this theorem, decidability of real number equality is sometimes called "analytic WLPO". WLPO is known to not be provable in IZF (and most constructive foundations), so this theorem establishes that we will be unable to prove an analogue to qdceq 10212 for real numbers. (Contributed by Jim Kingdon, 20-Jun-2024.) |
DECID WOmni | ||
Theorem | tridceq 14251* | Real trichotomy implies decidability of real number equality. Or in other words, analytic LPO implies analytic WLPO (see trilpo 14238 and redcwlpo 14250). Thus, this is an analytic analogue to lpowlpo 7153. (Contributed by Jim Kingdon, 24-Jul-2024.) |
DECID | ||
Theorem | redc0 14252* | Two ways to express decidability of real number equality. (Contributed by Jim Kingdon, 23-Jul-2024.) |
DECID DECID | ||
Theorem | reap0 14253* | Real number trichotomy is equivalent to decidability of apartness from zero. (Contributed by Jim Kingdon, 27-Jul-2024.) |
DECID # | ||
Theorem | dceqnconst 14254* | Decidability of real number equality implies the existence of a certain non-constant function from real numbers to integers. Variation of Exercise 11.6(i) of [HoTT], p. (varies). See redcwlpo 14250 for more discussion of decidability of real number equality. (Contributed by BJ and Jim Kingdon, 24-Jun-2024.) (Revised by Jim Kingdon, 23-Jul-2024.) |
DECID | ||
Theorem | dcapnconst 14255* |
Decidability of real number apartness implies the existence of a certain
non-constant function from real numbers to integers. Variation of
Exercise 11.6(i) of [HoTT], p. (varies).
See trilpo 14238 for more
discussion of decidability of real number apartness.
This is a weaker form of dceqnconst 14254 and in fact this theorem can be proved using dceqnconst 14254 as shown at dcapnconstALT 14256. (Contributed by BJ and Jim Kingdon, 24-Jun-2024.) |
DECID # | ||
Theorem | dcapnconstALT 14256* | Decidability of real number apartness implies the existence of a certain non-constant function from real numbers to integers. A proof of dcapnconst 14255 by means of dceqnconst 14254. (Contributed by Jim Kingdon, 27-Jul-2024.) (New usage is discouraged.) (Proof modification is discouraged.) |
DECID # | ||
Theorem | nconstwlpolem0 14257* | Lemma for nconstwlpo 14260. If all the terms of the series are zero, so is their sum. (Contributed by Jim Kingdon, 26-Jul-2024.) |
Theorem | nconstwlpolemgt0 14258* | Lemma for nconstwlpo 14260. If one of the terms of series is positive, so is the sum. (Contributed by Jim Kingdon, 26-Jul-2024.) |
Theorem | nconstwlpolem 14259* | Lemma for nconstwlpo 14260. (Contributed by Jim Kingdon, 23-Jul-2024.) |
Theorem | nconstwlpo 14260* | Existence of a certain non-constant function from reals to integers implies WOmni (the Weak Limited Principle of Omniscience or WLPO). Based on Exercise 11.6(ii) of [HoTT], p. (varies). (Contributed by BJ and Jim Kingdon, 22-Jul-2024.) |
WOmni | ||
Theorem | neapmkvlem 14261* | Lemma for neapmkv 14262. The result, with a few hypotheses broken out for convenience. (Contributed by Jim Kingdon, 25-Jun-2024.) |
# | ||
Theorem | neapmkv 14262* | If negated equality for real numbers implies apartness, Markov's Principle follows. Exercise 11.10 of [HoTT], p. (varies). (Contributed by Jim Kingdon, 24-Jun-2024.) |
# Markov | ||
Theorem | supfz 14263 | The supremum of a finite sequence of integers. (Contributed by Scott Fenton, 8-Aug-2013.) (Revised by Jim Kingdon, 15-Oct-2022.) |
Theorem | inffz 14264 | The infimum of a finite sequence of integers. (Contributed by Scott Fenton, 8-Aug-2013.) (Revised by Jim Kingdon, 15-Oct-2022.) |
inf | ||
Theorem | taupi 14265 | Relationship between and . This can be seen as connecting the ratio of a circle's circumference to its radius and the ratio of a circle's circumference to its diameter. (Contributed by Jim Kingdon, 19-Feb-2019.) (Revised by AV, 1-Oct-2020.) |
Theorem | ax1hfs 14266 | Heyting's formal system Axiom #1 from [Heyting] p. 127. (Contributed by MM, 11-Aug-2018.) |
Theorem | dftest 14267 |
A proposition is testable iff its negative or double-negative is true.
See Chapter 2 [Moschovakis] p. 2.
We do not formally define testability with a new token, but instead use DECID before the formula in question. For example, DECID corresponds to " is testable". (Contributed by David A. Wheeler, 13-Aug-2018.) For statements about testable propositions, search for the keyword "testable" in the comments of statements, for instance using the Metamath command "MM> SEARCH * "testable" / COMMENTS". (New usage is discouraged.) |
DECID | ||
These are definitions and proofs involving an experimental "allsome" quantifier (aka "all some"). In informal language, statements like "All Martians are green" imply that there is at least one Martian. But it's easy to mistranslate informal language into formal notations because similar statements like do not imply that is ever true, leading to vacuous truths. Some systems include a mechanism to counter this, e.g., PVS allows types to be appended with "+" to declare that they are nonempty. This section presents a different solution to the same problem. The "allsome" quantifier expressly includes the notion of both "all" and "there exists at least one" (aka some), and is defined to make it easier to more directly express both notions. The hope is that if a quantifier more directly expresses this concept, it will be used instead and reduce the risk of creating formal expressions that look okay but in fact are mistranslations. The term "allsome" was chosen because it's short, easy to say, and clearly hints at the two concepts it combines. I do not expect this to be used much in metamath, because in metamath there's a general policy of avoiding the use of new definitions unless there are very strong reasons to do so. Instead, my goal is to rigorously define this quantifier and demonstrate a few basic properties of it. The syntax allows two forms that look like they would be problematic, but they are fine. When applied to a top-level implication we allow ! , and when restricted (applied to a class) we allow ! . The first symbol after the setvar variable must always be if it is the form applied to a class, and since cannot begin a wff, it is unambiguous. The looks like it would be a problem because or might include implications, but any implication arrow within any wff must be surrounded by parentheses, so only the implication arrow of ! can follow the wff. The implication syntax would work fine without the parentheses, but I added the parentheses because it makes things clearer inside larger complex expressions, and it's also more consistent with the rest of the syntax. For more, see "The Allsome Quantifier" by David A. Wheeler at https://dwheeler.com/essays/allsome.html I hope that others will eventually agree that allsome is awesome. | ||
Syntax | walsi 14268 | Extend wff definition to include "all some" applied to a top-level implication, which means is true whenever is true, and there is at least least one where is true. (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Syntax | walsc 14269 | Extend wff definition to include "all some" applied to a class, which means is true for all in , and there is at least one in . (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Definition | df-alsi 14270 | Define "all some" applied to a top-level implication, which means is true whenever is true and there is at least one where is true. (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Definition | df-alsc 14271 | Define "all some" applied to a class, which means is true for all in and there is at least one in . (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Theorem | alsconv 14272 | There is an equivalence between the two "all some" forms. (Contributed by David A. Wheeler, 22-Oct-2018.) |
! ! | ||
Theorem | alsi1d 14273 | Deduction rule: Given "all some" applied to a top-level inference, you can extract the "for all" part. (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Theorem | alsi2d 14274 | Deduction rule: Given "all some" applied to a top-level inference, you can extract the "exists" part. (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Theorem | alsc1d 14275 | Deduction rule: Given "all some" applied to a class, you can extract the "for all" part. (Contributed by David A. Wheeler, 20-Oct-2018.) |
! | ||
Theorem | alsc2d 14276 | Deduction rule: Given "all some" applied to a class, you can extract the "there exists" part. (Contributed by David A. Wheeler, 20-Oct-2018.) |
! |
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