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**Theorem List for Intuitionistic Logic Explorer -** 14901-14994 *Has distinct variable group(s)
Type	Label	Description
Statement

Theorem	sscoll2 14901*	Version of ax-sscoll 14900 with two disjoint variable conditions removed and without initial universal quantifiers. (Contributed by BJ, 5-Oct-2019.)
$/\$

12.2.14 Real numbers

Axiom	ax-ddkcomp 14902	Axiom of Dedekind completeness for Dedekind real numbers: every inhabited upper-bounded located set of reals has a real upper bound. Ideally, this axiom should be "proved" as "axddkcomp" for the real numbers constructed from IZF, and then Axiom ax-ddkcomp 14902 should be used in place of construction specific results. In particular, axcaucvg 7902 should be proved from it. (Contributed by BJ, 24-Oct-2021.)
$/\$ $/\$ $/\$ $\/$ $/\$ $/\$

12.3 Mathbox for Jim Kingdon

12.3.1 Propositional and predicate logic

Theorem	nnnotnotr 14903	Double negation of double negation elimination. Suggested by an online post by Martin Escardo. Although this statement resembles nnexmid 850, it can be proved with reference only to implication and negation (that is, without use of disjunction). (Contributed by Jim Kingdon, 21-Oct-2024.)


12.3.2 Natural numbers

Theorem	1dom1el 14904	If a set is dominated by one, then any two of its elements are equal. (Contributed by Jim Kingdon, 23-Apr-2025.)
$/\$ $/\$

Theorem	ss1oel2o 14905	Any subset of ordinal one being an element of ordinal two is equivalent to excluded middle. A variation of exmid01 4200 which more directly illustrates the contrast with el2oss1o 6447. (Contributed by Jim Kingdon, 8-Aug-2022.)
EXMID

Theorem	nnti 14906	Ordering on a natural number generates a tight apartness. (Contributed by Jim Kingdon, 7-Aug-2022.)
$/\$ $/\$ $/\$

Theorem	012of 14907	Mapping zero and one between and style integers. (Contributed by Jim Kingdon, 28-Jun-2024.)
frec

Theorem	2o01f 14908	Mapping zero and one between and style integers. (Contributed by Jim Kingdon, 28-Jun-2024.)
frec

12.3.3 The power set of a singleton

Theorem	pwtrufal 14909	A subset of the singleton cannot be anything other than or . Removing the double negation would change the meaning, as seen at exmid01 4200. If we view a subset of a singleton as a truth value (as seen in theorems like exmidexmid 4198), then this theorem states there are no truth values other than true and false, as described in section 1.1 of [Bauer], p. 481. (Contributed by Mario Carneiro and Jim Kingdon, 11-Sep-2023.)
$\/$

Theorem	pwle2 14910*	An exercise related to copies of a singleton and the power set of a singleton (where the latter can also be thought of as representing truth values). Posed as an exercise by Martin Escardo online. (Contributed by Jim Kingdon, 3-Sep-2023.)
$/\$

Theorem	pwf1oexmid 14911*	An exercise related to copies of a singleton and the power set of a singleton (where the latter can also be thought of as representing truth values). Posed as an exercise by Martin Escardo online. (Contributed by Jim Kingdon, 3-Sep-2023.)
$/\$ $/\$ EXMID

Theorem	subctctexmid 14912*	If every subcountable set is countable and Markov's principle holds, excluded middle follows. Proposition 2.6 of [BauerSwan], p. 14:4. The proof is taken from that paper. (Contributed by Jim Kingdon, 29-Nov-2023.)
$/\$ ⊔ Markov EXMID

Theorem	sssneq 14913*	Any two elements of a subset of a singleton are equal. (Contributed by Jim Kingdon, 28-May-2024.)


Theorem	pw1nct 14914*	A condition which ensures that the powerset of a singleton is not countable. The antecedent here can be referred to as the uniformity principle. Based on Mastodon posts by Andrej Bauer and Rahul Chhabra. (Contributed by Jim Kingdon, 29-May-2024.)
⊔

12.3.4 Omniscience of NN+oo

Theorem	0nninf 14915	The zero element of ℕ_∞ (the constant sequence equal to ). (Contributed by Jim Kingdon, 14-Jul-2022.)
ℕ_∞

Theorem	nnsf 14916*	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 14917*	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 14918*	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 14919*	Lemma for nninfall 14920. (Contributed by Jim Kingdon, 1-Aug-2022.)
ℕ_∞ ℕ_∞

Theorem	nninfall 14920*	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 14921*	Lemma for nninfself 14924. Showing that the selection function is well defined. (Contributed by Jim Kingdon, 8-Aug-2022.)
ℕ_∞ $/\$ DECID

Theorem	nninfsellemcl 14922*	Lemma for nninfself 14924. (Contributed by Jim Kingdon, 8-Aug-2022.)
ℕ_∞ $/\$

Theorem	nninfsellemsuc 14923*	Lemma for nninfself 14924. (Contributed by Jim Kingdon, 6-Aug-2022.)
ℕ_∞ $/\$

Theorem	nninfself 14924*	Domain and range of the selection function for ℕ_∞. (Contributed by Jim Kingdon, 6-Aug-2022.)
ℕ_∞ ℕ_∞ℕ_∞

Theorem	nninfsellemeq 14925*	Lemma for nninfsel 14928. (Contributed by Jim Kingdon, 9-Aug-2022.)
ℕ_∞ ℕ_∞

Theorem	nninfsellemqall 14926*	Lemma for nninfsel 14928. (Contributed by Jim Kingdon, 9-Aug-2022.)
ℕ_∞ ℕ_∞

Theorem	nninfsellemeqinf 14927*	Lemma for nninfsel 14928. (Contributed by Jim Kingdon, 9-Aug-2022.)
ℕ_∞ ℕ_∞

Theorem	nninfsel 14928*	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 14929*	Lemma for nninfomni 14930. (Contributed by Jim Kingdon, 10-Aug-2022.)
ℕ_∞ ℕ_∞ Omni

Theorem	nninfomni 14930	ℕ_∞ is omniscient. Corollary 3.7 of [PradicBrown2022], p. 5. (Contributed by Jim Kingdon, 10-Aug-2022.)
ℕ_∞ Omni

Theorem	nninffeq 14931*	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_∞

12.3.5 Schroeder-Bernstein Theorem

Theorem	exmidsbthrlem 14932*	Lemma for exmidsbthr 14933. (Contributed by Jim Kingdon, 11-Aug-2022.)
ℕ_∞ $/\$ EXMID

Theorem	exmidsbthr 14933*	The Schroeder-Bernstein Theorem implies excluded middle. Theorem 1 of [PradicBrown2022], p. 1. (Contributed by Jim Kingdon, 11-Aug-2022.)
$/\$ EXMID

Theorem	exmidsbth 14934*	The Schroeder-Bernstein Theorem is equivalent to excluded middle. This is Metamath 100 proof #25. The forward direction (isbth 6969) 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 6969. The reverse direction (exmidsbthr 14933) 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 14935	Lemma for sbthom 14936. (Contributed by Mario Carneiro and Jim Kingdon, 13-Jul-2023.)
Omni ⊔ $\/$

Theorem	sbthom 14936	Schroeder-Bernstein is not possible even for . We know by exmidsbth 14934 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

12.3.6 Real and complex numbers

Theorem	qdencn 14937*	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 11214 (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 14938*	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 14939	Two ways of stating real number trichotomy. (Contributed by Jim Kingdon, 23-Aug-2023.)
$/\$ $\/$ $\/$ DECID #

Theorem	isomninnlem 14940*	Lemma for isomninn 14941. The result, with a hypothesis to provide a convenient notation. (Contributed by Jim Kingdon, 30-Aug-2023.)
frec Omni $\/$

Theorem	isomninn 14941*	Omniscience stated in terms of natural numbers. Similar to isomnimap 7138 but it will sometimes be more convenient to use and rather than and . (Contributed by Jim Kingdon, 30-Aug-2023.)
Omni $\/$

Theorem	cvgcmp2nlemabs 14942*	Lemma for cvgcmp2n 14943. 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 14943*	A comparison test for convergence of a real infinite series. (Contributed by Jim Kingdon, 25-Aug-2023.)
$/\$ $/\$ $/\$

Theorem	iooref1o 14944	A one-to-one mapping from the real numbers onto the open unit interval. (Contributed by Jim Kingdon, 27-Jun-2024.)


Theorem	iooreen 14945	An open interval is equinumerous to the real numbers. (Contributed by Jim Kingdon, 27-Jun-2024.)


12.3.7 Analytic omniscience principles 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 7143), (1) the Limited Principle of Omniscience (LPO) is Omni (see df-omni 7136), (2) the Weak Limited Principle of Omniscience (WLPO) is WOmni (see df-womni 7165), (3) Markov's Principle (MP) is Markov (see df-markov 7153), (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 14953), (2) Analytic WLPO is decidability of real number equality, DECID (see redcwlpo 14965), (3) Analytic MP is # (see neapmkv 14978), (4) Analytic LLPO is real number dichotomy, $\/$ (most relevant current theorem is maxclpr 11234).

Theorem	trilpolemclim 14946*	Lemma for trilpo 14953. Convergence of the series. (Contributed by Jim Kingdon, 24-Aug-2023.)


Theorem	trilpolemcl 14947*	Lemma for trilpo 14953. The sum exists. (Contributed by Jim Kingdon, 23-Aug-2023.)


Theorem	trilpolemisumle 14948*	Lemma for trilpo 14953. An upper bound for the sum of the digits beyond a certain point. (Contributed by Jim Kingdon, 28-Aug-2023.)


Theorem	trilpolemgt1 14949*	Lemma for trilpo 14953. The case. (Contributed by Jim Kingdon, 23-Aug-2023.)


Theorem	trilpolemeq1 14950*	Lemma for trilpo 14953. 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 14951*	Lemma for trilpo 14953. 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 7141 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 14952*	Lemma for trilpo 14953. The result. (Contributed by Jim Kingdon, 23-Aug-2023.)
$\/$ $\/$ $\/$

Theorem	trilpo 14953*	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 14951 (which means the sequence contains a zero), trilpolemeq1 14950 (which means the sequence is all ones), and trilpolemgt1 14949 (which is not possible). Equivalent ways to state real number trichotomy (sometimes called "analytic LPO") include decidability of real number apartness (see triap 14939) or that the real numbers are a discrete field (see trirec0 14954). 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 10246 for real numbers. (Contributed by Jim Kingdon, 23-Aug-2023.)
$\/$ $\/$ Omni

Theorem	trirec0 14954*	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 14953). (Contributed by Jim Kingdon, 10-Jun-2024.)
$\/$ $\/$ $\/$

Theorem	trirec0xor 14955*	Version of trirec0 14954 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 14956	Lemma for apdiff 14958. 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 14957	Lemma for apdiff 14958. (Contributed by Jim Kingdon, 19-May-2024.)
# $/\$ # #

Theorem	apdiff 14958*	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 14959*	Lemma for iswomnimap 7167. The result, with a hypothesis for convenience. (Contributed by Jim Kingdon, 20-Jun-2024.)
frec WOmni DECID

Theorem	iswomninn 14960*	Weak omniscience stated in terms of natural numbers. Similar to iswomnimap 7167 but it will sometimes be more convenient to use and rather than and . (Contributed by Jim Kingdon, 20-Jun-2024.)
WOmni DECID

Theorem	iswomni0 14961*	Weak omniscience stated in terms of equality with . Like iswomninn 14960 but with zero in place of one. (Contributed by Jim Kingdon, 24-Jul-2024.)
WOmni DECID

Theorem	ismkvnnlem 14962*	Lemma for ismkvnn 14963. 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 14963*	The predicate of being Markov stated in terms of set exponentiation. (Contributed by Jim Kingdon, 25-Jun-2024.)
Markov

Theorem	redcwlpolemeq1 14964*	Lemma for redcwlpo 14965. A biconditionalized version of trilpolemeq1 14950. (Contributed by Jim Kingdon, 21-Jun-2024.)


Theorem	redcwlpo 14965*	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 14964). 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 10250 for real numbers. (Contributed by Jim Kingdon, 20-Jun-2024.)
DECID WOmni

Theorem	tridceq 14966*	Real trichotomy implies decidability of real number equality. Or in other words, analytic LPO implies analytic WLPO (see trilpo 14953 and redcwlpo 14965). Thus, this is an analytic analogue to lpowlpo 7169. (Contributed by Jim Kingdon, 24-Jul-2024.)
$\/$ $\/$ DECID

Theorem	redc0 14967*	Two ways to express decidability of real number equality. (Contributed by Jim Kingdon, 23-Jul-2024.)
DECID DECID

Theorem	reap0 14968*	Real number trichotomy is equivalent to decidability of apartness from zero. (Contributed by Jim Kingdon, 27-Jul-2024.)
$\/$ $\/$ DECID #

Theorem	cndcap 14969*	Real number trichotomy is equivalent to decidability of complex number apartness. (Contributed by Jim Kingdon, 10-Apr-2025.)
$\/$ $\/$ DECID #

Theorem	dceqnconst 14970*	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 14965 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 14971*	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 14953 for more discussion of decidability of real number apartness. This is a weaker form of dceqnconst 14970 and in fact this theorem can be proved using dceqnconst 14970 as shown at dcapnconstALT 14972. (Contributed by BJ and Jim Kingdon, 24-Jun-2024.)
DECID # $/\$ $/\$

Theorem	dcapnconstALT 14972*	Decidability of real number apartness implies the existence of a certain non-constant function from real numbers to integers. A proof of dcapnconst 14971 by means of dceqnconst 14970. (Contributed by Jim Kingdon, 27-Jul-2024.) (New usage is discouraged.) (Proof modification is discouraged.)
DECID # $/\$ $/\$

Theorem	nconstwlpolem0 14973*	Lemma for nconstwlpo 14976. If all the terms of the series are zero, so is their sum. (Contributed by Jim Kingdon, 26-Jul-2024.)


Theorem	nconstwlpolemgt0 14974*	Lemma for nconstwlpo 14976. If one of the terms of series is positive, so is the sum. (Contributed by Jim Kingdon, 26-Jul-2024.)


Theorem	nconstwlpolem 14975*	Lemma for nconstwlpo 14976. (Contributed by Jim Kingdon, 23-Jul-2024.)
$/\$ $\/$

Theorem	nconstwlpo 14976*	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 14977*	Lemma for neapmkv 14978. The result, with a few hypotheses broken out for convenience. (Contributed by Jim Kingdon, 25-Jun-2024.)
$/\$ #

Theorem	neapmkv 14978*	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	neap0mkv 14979*	The analytic Markov principle can be expressed either with two arbitrary real numbers, or one arbitrary number and zero. (Contributed by Jim Kingdon, 23-Feb-2025.)
# #

Theorem	ltlenmkv 14980*	If can be expressed as holding exactly when holds and the values are not equal, then the analytic Markov's Principle applies. (To get the regular Markov's Principle, combine with neapmkv 14978). (Contributed by Jim Kingdon, 23-Feb-2025.)
$/\$ #

12.3.8 Supremum and infimum

Theorem	supfz 14981	The supremum of a finite sequence of integers. (Contributed by Scott Fenton, 8-Aug-2013.) (Revised by Jim Kingdon, 15-Oct-2022.)


Theorem	inffz 14982	The infimum of a finite sequence of integers. (Contributed by Scott Fenton, 8-Aug-2013.) (Revised by Jim Kingdon, 15-Oct-2022.)
inf

12.3.9 Circle constant

Theorem	taupi 14983	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.)


12.4 Mathbox for Mykola Mostovenko

Theorem	ax1hfs 14984	Heyting's formal system Axiom #1 from [Heyting] p. 127. (Contributed by MM, 11-Aug-2018.)
$/\$

12.5 Mathbox for David A. Wheeler

12.5.1 Testable propositions

Theorem	dftest 14985	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 $\/$

12.5.2 Allsome quantifier 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 14986	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 14987	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 14988	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 14989	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 14990	There is an equivalence between the two "all some" forms. (Contributed by David A. Wheeler, 22-Oct-2018.)
! !

Theorem	alsi1d 14991	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 14992	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 14993	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 14994	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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