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Type | Label | Description | ||||||||||||||||||||||||
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Statement | ||||||||||||||||||||||||||
Theorem | negfcncf 12501* | The negative of a continuous complex function is continuous. (Contributed by Paul Chapman, 21-Jan-2008.) (Revised by Mario Carneiro, 25-Aug-2014.) | ||||||||||||||||||||||||
Theorem | mulcncflem 12502* | Lemma for mulcncf 12503. (Contributed by Jim Kingdon, 29-May-2023.) | ||||||||||||||||||||||||
Theorem | mulcncf 12503* | The multiplication of two continuous complex functions is continuous. (Contributed by Glauco Siliprandi, 29-Jun-2017.) | ||||||||||||||||||||||||
Theorem | expcncf 12504* | The power function on complex numbers, for fixed exponent N, is continuous. (Contributed by Glauco Siliprandi, 29-Jun-2017.) | ||||||||||||||||||||||||
Syntax | climc 12505 | The limit operator. | ||||||||||||||||||||||||
lim | ||||||||||||||||||||||||||
Syntax | cdv 12506 | The derivative operator. | ||||||||||||||||||||||||
Definition | df-limced 12507* | Define the set of limits of a complex function at a point. Under normal circumstances, this will be a singleton or empty, depending on whether the limit exists. (Contributed by Mario Carneiro, 24-Dec-2016.) (Revised by Jim Kingdon, 3-Jun-2023.) | ||||||||||||||||||||||||
lim # | ||||||||||||||||||||||||||
Definition | df-dvap 12508* | Define the derivative operator. This acts on functions to produce a function that is defined where the original function is differentiable, with value the derivative of the function at these points. The set here is the ambient topological space under which we are evaluating the continuity of the difference quotient. Although the definition is valid for any subset of and is well-behaved when contains no isolated points, we will restrict our attention to the cases or for the majority of the development, these corresponding respectively to real and complex differentiation. (Contributed by Mario Carneiro, 7-Aug-2014.) (Revised by Jim Kingdon, 25-Jun-2023.) | ||||||||||||||||||||||||
↾_{t} # lim | ||||||||||||||||||||||||||
Theorem | limcrcl 12509 | Reverse closure for the limit operator. (Contributed by Mario Carneiro, 28-Dec-2016.) | ||||||||||||||||||||||||
lim | ||||||||||||||||||||||||||
Theorem | limccl 12510 | Closure of the limit operator. (Contributed by Mario Carneiro, 25-Dec-2016.) | ||||||||||||||||||||||||
lim | ||||||||||||||||||||||||||
Theorem | ellimc3ap 12511* | Write the epsilon-delta definition of a limit. (Contributed by Mario Carneiro, 28-Dec-2016.) Use apartness. (Revised by Jim Kingdon, 3-Jun-2023.) | ||||||||||||||||||||||||
lim # | ||||||||||||||||||||||||||
Theorem | limcdifap 12512* | It suffices to consider functions which are not defined at to define the limit of a function. In particular, the value of the original function at does not affect the limit of . (Contributed by Mario Carneiro, 25-Dec-2016.) (Revised by Jim Kingdon, 3-Jun-2023.) | ||||||||||||||||||||||||
lim # lim | ||||||||||||||||||||||||||
Theorem | limcimolemlt 12513* | Lemma for limcimo 12514. (Contributed by Jim Kingdon, 3-Jul-2023.) | ||||||||||||||||||||||||
↾_{t} # lim lim # # | ||||||||||||||||||||||||||
Theorem | limcimo 12514* | Conditions which ensure there is at most one limit value of at . (Contributed by Mario Carneiro, 25-Dec-2016.) (Revised by Jim Kingdon, 8-Jul-2023.) | ||||||||||||||||||||||||
↾_{t} # lim | ||||||||||||||||||||||||||
Theorem | limcresi 12515 | Any limit of is also a limit of the restriction of . (Contributed by Mario Carneiro, 28-Dec-2016.) | ||||||||||||||||||||||||
lim lim | ||||||||||||||||||||||||||
Theorem | cnplimcim 12516 | If a function is continuous at , its limit at equals the value of the function there. (Contributed by Mario Carneiro, 28-Dec-2016.) (Revised by Jim Kingdon, 14-Jun-2023.) | ||||||||||||||||||||||||
↾_{t} lim | ||||||||||||||||||||||||||
Theorem | cnlimcim 12517* | If is a continuous function, the limit of the function at each point equals the value of the function. (Contributed by Mario Carneiro, 28-Dec-2016.) (Revised by Jim Kingdon, 16-Jun-2023.) | ||||||||||||||||||||||||
lim | ||||||||||||||||||||||||||
Theorem | cnlimci 12518 | If is a continuous function, then the limit of the function at any point equals its value. (Contributed by Mario Carneiro, 28-Dec-2016.) | ||||||||||||||||||||||||
lim | ||||||||||||||||||||||||||
Theorem | cnmptlimc 12519* | If is a continuous function, then the limit of the function at any point equals its value. (Contributed by Mario Carneiro, 28-Dec-2016.) | ||||||||||||||||||||||||
lim | ||||||||||||||||||||||||||
Theorem | limccnpcntop 12520 | If the limit of at is and is continuous at , then the limit of at is . (Contributed by Mario Carneiro, 28-Dec-2016.) (Revised by Jim Kingdon, 18-Jun-2023.) | ||||||||||||||||||||||||
↾_{t} lim lim | ||||||||||||||||||||||||||
Theorem | reldvg 12521 | The derivative function is a relation. (Contributed by Mario Carneiro, 7-Aug-2014.) (Revised by Jim Kingdon, 25-Jun-2023.) | ||||||||||||||||||||||||
Theorem | dvlemap 12522* | Closure for a difference quotient. (Contributed by Mario Carneiro, 1-Sep-2014.) (Revised by Jim Kingdon, 27-Jun-2023.) | ||||||||||||||||||||||||
# | ||||||||||||||||||||||||||
Theorem | dvfvalap 12523* | Value and set bounds on the derivative operator. (Contributed by Mario Carneiro, 7-Aug-2014.) (Revised by Jim Kingdon, 27-Jun-2023.) | ||||||||||||||||||||||||
↾_{t} # lim | ||||||||||||||||||||||||||
Theorem | eldvap 12524* | The differentiable predicate. A function is differentiable at with derivative iff is defined in a neighborhood of and the difference quotient has limit at . (Contributed by Mario Carneiro, 7-Aug-2014.) (Revised by Jim Kingdon, 27-Jun-2023.) | ||||||||||||||||||||||||
↾_{t} # lim | ||||||||||||||||||||||||||
Theorem | dvcl 12525 | The derivative function takes values in the complex numbers. (Contributed by Mario Carneiro, 7-Aug-2014.) (Revised by Mario Carneiro, 9-Feb-2015.) | ||||||||||||||||||||||||
Theorem | dvbssntrcntop 12526 | The set of differentiable points is a subset of the interior of the domain of the function. (Contributed by Mario Carneiro, 7-Aug-2014.) (Revised by Jim Kingdon, 27-Jun-2023.) | ||||||||||||||||||||||||
↾_{t} | ||||||||||||||||||||||||||
Theorem | dvbss 12527 | The set of differentiable points is a subset of the domain of the function. (Contributed by Mario Carneiro, 6-Aug-2014.) (Revised by Mario Carneiro, 9-Feb-2015.) | ||||||||||||||||||||||||
Theorem | dvbsssg 12528 | The set of differentiable points is a subset of the ambient topology. (Contributed by Mario Carneiro, 18-Mar-2015.) (Revised by Jim Kingdon, 28-Jun-2023.) | ||||||||||||||||||||||||
Theorem | recnprss 12529 | Both and are subsets of . (Contributed by Mario Carneiro, 10-Feb-2015.) | ||||||||||||||||||||||||
Theorem | dvfgg 12530 | Explicitly write out the functionality condition on derivative for and . (Contributed by Mario Carneiro, 9-Feb-2015.) (Revised by Jim Kingdon, 28-Jun-2023.) | ||||||||||||||||||||||||
Theorem | dvfpm 12531 | The derivative is a function. (Contributed by Mario Carneiro, 8-Aug-2014.) (Revised by Jim Kingdon, 28-Jul-2023.) | ||||||||||||||||||||||||
Theorem | dvfcnpm 12532 | The derivative is a function. (Contributed by Mario Carneiro, 9-Feb-2015.) (Revised by Jim Kingdon, 28-Jul-2023.) | ||||||||||||||||||||||||
Theorem | dvidlemap 12533* | Lemma for dvid 12535 and dvconst 12534. (Contributed by Mario Carneiro, 8-Aug-2014.) (Revised by Jim Kingdon, 2-Aug-2023.) | ||||||||||||||||||||||||
# | ||||||||||||||||||||||||||
Theorem | dvconst 12534 | Derivative of a constant function. (Contributed by Mario Carneiro, 8-Aug-2014.) (Revised by Jim Kingdon, 2-Aug-2023.) | ||||||||||||||||||||||||
Theorem | dvid 12535 | Derivative of the identity function. (Contributed by Mario Carneiro, 8-Aug-2014.) (Revised by Jim Kingdon, 2-Aug-2023.) | ||||||||||||||||||||||||
This section describes the conventions we use. However, these conventions often refer to existing mathematical practices, which are discussed in more detail in other references. The following sources lay out how mathematics is developed without the law of the excluded middle. Of course, there are a greater number of sources which assume excluded middle and most of what is in them applies here too (especially in a treatment such as ours which is built on first order logic and set theory, rather than, say, type theory). Studying how a topic is treated in the Metamath Proof Explorer and the references therein is often a good place to start (and is easy to compare with the Intuitionistic Logic Explorer). The textbooks provide a motivation for what we are doing, whereas Metamath lets you see in detail all hidden and implicit steps. Most standard theorems are accompanied by citations. Some closely followed texts include the following:
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Theorem | conventions 12536 |
Unless there is a reason to diverge, we follow the conventions of the
Metamath Proof Explorer (MPE, 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.
Label naming conventions Here are a few of the label naming conventions:
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. For the "g" abbreviation, this is related to the set.mm usage, in which "is a set" conditions are converted from hypotheses to antecedents, but is also used where "is a set" conditions are added relative to similar set.mm theorems.
(Contributed by Jim Kingdon, 24-Feb-2020.) | ||||||||||||||||||||||||
Theorem | ex-or 12537 | Example for ax-io 671. Example by David A. Wheeler. (Contributed by Mario Carneiro, 9-May-2015.) | ||||||||||||||||||||||||
Theorem | ex-an 12538 | Example for ax-ia1 105. Example by David A. Wheeler. (Contributed by Mario Carneiro, 9-May-2015.) | ||||||||||||||||||||||||
Theorem | 1kp2ke3k 12539 |
Example for df-dec 9035, 1000 + 2000 = 3000.
This proof disproves (by counterexample) the assertion of Hao Wang, who stated, "There is a theorem in the primitive notation of set theory that corresponds to the arithmetic theorem 1000 + 2000 = 3000. The formula would be forbiddingly long... even if (one) knows the definitions and is asked to simplify the long formula according to them, chances are he will make errors and arrive at some incorrect result." (Hao Wang, "Theory and practice in mathematics" , In Thomas Tymoczko, editor, New Directions in the Philosophy of Mathematics, pp 129-152, Birkauser Boston, Inc., Boston, 1986. (QA8.6.N48). The quote itself is on page 140.) This is noted in Metamath: A Computer Language for Pure Mathematics by Norman Megill (2007) section 1.1.3. Megill then states, "A number of writers have conveyed the impression that the kind of absolute rigor provided by Metamath is an impossible dream, suggesting that a complete, formal verification of a typical theorem would take millions of steps in untold volumes of books... These writers assume, however, that in order to achieve the kind of complete formal verification they desire one must break down a proof into individual primitive steps that make direct reference to the axioms. This is not necessary. There is no reason not to make use of previously proved theorems rather than proving them over and over... A hierarchy of theorems and definitions permits an exponential growth in the formula sizes and primitive proof steps to be described with only a linear growth in the number of symbols used. Of course, this is how ordinary informal mathematics is normally done anyway, but with Metamath it can be done with absolute rigor and precision." The proof here starts with , commutes it, and repeatedly multiplies both sides by ten. This is certainly longer than traditional mathematical proofs, e.g., there are a number of steps explicitly shown here to show that we're allowed to do operations such as multiplication. However, while longer, the proof is clearly a manageable size - even though every step is rigorously derived all the way back to the primitive notions of set theory and logic. And while there's a risk of making errors, the many independent verifiers make it much less likely that an incorrect result will be accepted. This proof heavily relies on the decimal constructor df-dec 9035 developed by Mario Carneiro in 2015. The underlying Metamath language has an intentionally very small set of primitives; it doesn't even have a built-in construct for numbers. Instead, the digits are defined using these primitives, and the decimal constructor is used to make it easy to express larger numbers as combinations of digits. (Contributed by David A. Wheeler, 29-Jun-2016.) (Shortened by Mario Carneiro using the arithmetic algorithm in mmj2, 30-Jun-2016.) | ||||||||||||||||||||||||
;;; ;;; ;;; | ||||||||||||||||||||||||||
Theorem | ex-fl 12540 | Example for df-fl 9884. Example by David A. Wheeler. (Contributed by Mario Carneiro, 18-Jun-2015.) | ||||||||||||||||||||||||
Theorem | ex-ceil 12541 | Example for df-ceil 9885. (Contributed by AV, 4-Sep-2021.) | ||||||||||||||||||||||||
⌈ ⌈ | ||||||||||||||||||||||||||
Theorem | ex-exp 12542 | Example for df-exp 10134. (Contributed by AV, 4-Sep-2021.) | ||||||||||||||||||||||||
; | ||||||||||||||||||||||||||
Theorem | ex-fac 12543 | Example for df-fac 10313. (Contributed by AV, 4-Sep-2021.) | ||||||||||||||||||||||||
;; | ||||||||||||||||||||||||||
Theorem | ex-bc 12544 | Example for df-bc 10335. (Contributed by AV, 4-Sep-2021.) | ||||||||||||||||||||||||
; | ||||||||||||||||||||||||||
Theorem | ex-dvds 12545 | Example for df-dvds 11289: 3 divides into 6. (Contributed by David A. Wheeler, 19-May-2015.) | ||||||||||||||||||||||||
Theorem | ex-gcd 12546 | Example for df-gcd 11431. (Contributed by AV, 5-Sep-2021.) | ||||||||||||||||||||||||
Theorem | mathbox 12547 |
(This theorem is a dummy placeholder for these guidelines. The name of
this theorem, "mathbox", is hard-coded into the Metamath
program to
identify the start of the mathbox section for web page generation.)
A "mathbox" is a user-contributed section that is maintained by its contributor independently from the main part of iset.mm. For contributors: By making a contribution, you agree to release it into the public domain, according to the statement at the beginning of iset.mm. Guidelines: Mathboxes in iset.mm follow the same practices as in set.mm, so refer to the mathbox guidelines there for more details. (Contributed by NM, 20-Feb-2007.) (Revised by the Metamath team, 9-Sep-2023.) (New usage is discouraged.) | ||||||||||||||||||||||||
Theorem | nnexmid 12548 | Double negation of excluded middle. Intuitionistic logic refutes the negation of excluded middle (but, of course, does not prove excluded middle) for any formula. (Contributed by BJ, 9-Oct-2019.) | ||||||||||||||||||||||||
Theorem | nndc 12549 | Double negation of decidability of a formula. Intuitionistic logic refutes undecidability (but, of course, does not prove decidability) of any formula. (Contributed by BJ, 9-Oct-2019.) | ||||||||||||||||||||||||
DECID | ||||||||||||||||||||||||||
Theorem | dcdc 12550 | Decidability of a proposition is decidable if and only if that proposition is decidable. DECID is idempotent. (Contributed by BJ, 9-Oct-2019.) | ||||||||||||||||||||||||
DECID DECID DECID | ||||||||||||||||||||||||||
Theorem | bj-ex 12551* | Existential generalization. (Contributed by BJ, 8-Dec-2019.) Proof modification is discouraged because there are shorter proofs, but using less basic results (like exlimiv 1545 and 19.9ht 1588 or 19.23ht 1441). (Proof modification is discouraged.) | ||||||||||||||||||||||||
Theorem | bj-hbalt 12552 | Closed form of hbal 1421 (copied from set.mm). (Contributed by BJ, 2-May-2019.) | ||||||||||||||||||||||||
Theorem | bj-nfalt 12553 | Closed form of nfal 1523 (copied from set.mm). (Contributed by BJ, 2-May-2019.) | ||||||||||||||||||||||||
Theorem | spimd 12554 | Deduction form of spim 1684. (Contributed by BJ, 17-Oct-2019.) | ||||||||||||||||||||||||
Theorem | 2spim 12555* | Double substitution, as in spim 1684. (Contributed by BJ, 17-Oct-2019.) | ||||||||||||||||||||||||
Theorem | ch2var 12556* | Implicit substitution of for and for into a theorem. (Contributed by BJ, 17-Oct-2019.) | ||||||||||||||||||||||||
Theorem | ch2varv 12557* | Version of ch2var 12556 with non-freeness hypotheses replaced with disjoint variable conditions. (Contributed by BJ, 17-Oct-2019.) | ||||||||||||||||||||||||
Theorem | bj-exlimmp 12558 | Lemma for bj-vtoclgf 12564. (Contributed by BJ, 21-Nov-2019.) (Proof modification is discouraged.) | ||||||||||||||||||||||||
Theorem | bj-exlimmpi 12559 | Lemma for bj-vtoclgf 12564. (Contributed by BJ, 21-Nov-2019.) (Proof modification is discouraged.) | ||||||||||||||||||||||||
Theorem | bj-sbimedh 12560 | A strengthening of sbiedh 1728 (same proof). (Contributed by BJ, 16-Dec-2019.) | ||||||||||||||||||||||||
Theorem | bj-sbimeh 12561 | A strengthening of sbieh 1731 (same proof). (Contributed by BJ, 16-Dec-2019.) | ||||||||||||||||||||||||
Theorem | bj-sbime 12562 | A strengthening of sbie 1732 (same proof). (Contributed by BJ, 16-Dec-2019.) | ||||||||||||||||||||||||
Various utility theorems using FOL and extensionality. | ||||||||||||||||||||||||||
Theorem | bj-vtoclgft 12563 | Weakening two hypotheses of vtoclgf 2699. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-vtoclgf 12564 | Weakening two hypotheses of vtoclgf 2699. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabgf0 12565 | Lemma for elabgf 2780. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabgft1 12566 | One implication of elabgf 2780, in closed form. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabgf1 12567 | One implication of elabgf 2780. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabgf2 12568 | One implication of elabgf 2780. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabf1 12569* | One implication of elabf 2781. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabf2 12570* | One implication of elabf 2781. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elab1 12571* | One implication of elab 2782. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elab2a 12572* | One implication of elab 2782. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | elabg2 12573* | One implication of elabg 2783. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-rspgt 12574 | Restricted specialization, generalized. Weakens a hypothesis of rspccv 2741 and seems to have a shorter proof. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-rspg 12575 | Restricted specialization, generalized. Weakens a hypothesis of rspccv 2741 and seems to have a shorter proof. (Contributed by BJ, 21-Nov-2019.) | ||||||||||||||||||||||||
Theorem | cbvrald 12576* | Rule used to change bound variables, using implicit substitution. (Contributed by BJ, 22-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-intabssel 12577 | Version of intss1 3733 using a class abstraction and explicit substitution. (Contributed by BJ, 29-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-intabssel1 12578 | Version of intss1 3733 using a class abstraction and implicit substitution. Closed form of intmin3 3745. (Contributed by BJ, 29-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-elssuniab 12579 | Version of elssuni 3711 using a class abstraction and explicit substitution. (Contributed by BJ, 29-Nov-2019.) | ||||||||||||||||||||||||
Theorem | bj-sseq 12580 | If two converse inclusions are characterized each by a formula, then equality is characterized by the conjunction of these formulas. (Contributed by BJ, 30-Nov-2019.) | ||||||||||||||||||||||||
The question of decidability is essential in intuitionistic logic. In intuitionistic set theories, it is natural to define decidability of a set (or class) as decidability of membership in it. One can parameterize this notion with another set (or class) since it is often important to assess decidability of membership in one class among elements of another class. Namely, one will say that " is decidable in " if DECID (see df-dcin 12582). Note the similarity with the definition of a bounded class as a class for which membership in it is a bounded proposition (df-bdc 12620). | ||||||||||||||||||||||||||
Syntax | wdcin 12581 | Syntax for decidability of a class in another. | ||||||||||||||||||||||||
DECID_{in} | ||||||||||||||||||||||||||
Definition | df-dcin 12582* | Define decidability of a class in another. (Contributed by BJ, 19-Feb-2022.) | ||||||||||||||||||||||||
DECID_{in} DECID | ||||||||||||||||||||||||||
Theorem | decidi 12583 | Property of being decidable in another class. (Contributed by BJ, 19-Feb-2022.) | ||||||||||||||||||||||||
DECID_{in} | ||||||||||||||||||||||||||
Theorem | decidr 12584* | Sufficient condition for being decidable in another class. (Contributed by BJ, 19-Feb-2022.) | ||||||||||||||||||||||||
DECID_{in} | ||||||||||||||||||||||||||
Theorem | decidin 12585 | If A is a decidable subclass of B (meaning: it is a subclass of B and it is decidable in B), and B is decidable in C, then A is decidable in C. (Contributed by BJ, 19-Feb-2022.) | ||||||||||||||||||||||||
DECID_{in} DECID_{in} DECID_{in} | ||||||||||||||||||||||||||
Theorem | uzdcinzz 12586 | An upperset of integers is decidable in the integers. Reformulation of eluzdc 9254. (Contributed by Jim Kingdon, 18-Apr-2020.) (Revised by BJ, 19-Feb-2022.) | ||||||||||||||||||||||||
DECID_{in} | ||||||||||||||||||||||||||
Theorem | sumdc2 12587* | Alternate proof of sumdc 10966, without disjoint variable condition on (longer because the statement is taylored to the proof sumdc 10966). (Contributed by BJ, 19-Feb-2022.) | ||||||||||||||||||||||||
DECID DECID | ||||||||||||||||||||||||||
Theorem | djucllem 12588* | Lemma for djulcl 6851 and djurcl 6852. (Contributed by BJ, 4-Jul-2022.) | ||||||||||||||||||||||||
Theorem | djulclALT 12589 | Shortening of djulcl 6851 using djucllem 12588. (Contributed by BJ, 4-Jul-2022.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||||||||||||
inl ⊔ | ||||||||||||||||||||||||||
Theorem | djurclALT 12590 | Shortening of djurcl 6852 using djucllem 12588. (Contributed by BJ, 4-Jul-2022.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||||||||||||
inr ⊔ | ||||||||||||||||||||||||||
This section develops constructive Zermelo--Fraenkel set theory (CZF) on top of intuitionistic logic. It is a constructive theory in the sense that its logic is intuitionistic and it is predicative. "Predicative" means that new sets can be constructed only from already constructed sets. In particular, the axiom of separation ax-sep 3986 is not predicative (because we cannot allow all formulas to define a subset) and is replaced in CZF by bounded separation ax-bdsep 12663. Because this axiom is weaker than full separation, the axiom of replacement or collection ax-coll 3983 of ZF and IZF has to be strengthened in CZF to the axiom of strong collection ax-strcoll 12765 (which is a theorem of IZF), and the axiom of infinity needs a more precise version, the von Neumann axiom of infinity ax-infvn 12724. Similarly, the axiom of powerset ax-pow 4038 is not predicative (checking whether a set is included in another requires to universally quantifier over that "not yet constructed" set) and is replaced in CZF by the axiom of fullness or the axiom of subset collection ax-sscoll 12770. In an intuitionistic context, the axiom of regularity is stated in IZF as well as in CZF as the axiom of set induction ax-setind 4390. It is sometimes interesting to study the weakening of CZF where that axiom is replaced by bounded set induction ax-bdsetind 12751. For more details on CZF, a useful set of notes is Peter Aczel and Michael Rathjen, CST Book draft. (available at http://www1.maths.leeds.ac.uk/~rathjen/book.pdf) and an interesting article is Michael Shulman, Comparing material and structural set theories, Annals of Pure and Applied Logic, Volume 170, Issue 4 (Apr. 2019), 465--504. (available at https://arxiv.org/abs/1808.05204) I also thank Michael Rathjen and Michael Shulman for useful hints in the formulation of some results. | ||||||||||||||||||||||||||
The present definition of bounded formulas emerged from a discussion on GitHub between Jim Kingdon, Mario Carneiro and I, started 23-Sept-2019 (see https://github.com/metamath/set.mm/issues/1173 and links therein). In order to state certain axiom schemes of Constructive Zermelo–Fraenkel (CZF) set theory, like the axiom scheme of bounded (or restricted, or Δ_{0}) separation, it is necessary to distinguish certain formulas, called bounded (or restricted, or Δ_{0}) formulas. The necessity of considering bounded formulas also arises in several theories of bounded arithmetic, both classical or intuitonistic, for instance to state the axiom scheme of Δ_{0}-induction. To formalize this in Metamath, there are several choices to make. A first choice is to either create a new type for bounded formulas, or to create a predicate on formulas that indicates whether they are bounded. In the first case, one creates a new type "wff0" with a new set of metavariables (ph_{0} ...) and an axiom "$a wff ph_{0} " ensuring that bounded formulas are formulas, so that one can reuse existing theorems, and then axioms take the form "$a wff0 ( ph_{0} -> ps_{0} )", etc. In the second case, one introduces a predicate "BOUNDED " with the intended meaning that "BOUNDED " is a formula meaning that is a bounded formula. We choose the second option, since the first would complicate the grammar, risking to make it ambiguous. (TODO: elaborate.) A second choice is to view "bounded" either as a syntactic or a semantic property. For instance, is not syntactically bounded since it has an unbounded universal quantifier, but it is semantically bounded since it is equivalent to which is bounded. We choose the second option, so that formulas using defined symbols can be proved bounded. A third choice is in the form of the axioms, either in closed form or in inference form. One cannot state all the axioms in closed form, especially ax-bd0 12592. Indeed, if we posited it in closed form, then we could prove for instance BOUNDED and BOUNDED which is problematic (with the law of excluded middle, this would entail that all formulas are bounded, but even without it, too many formulas could be proved bounded...). (TODO: elaborate.) Having ax-bd0 12592 in inference form ensures that a formula can be proved bounded only if it is equivalent *for all values of the free variables* to a syntactically bounded one. The other axioms (ax-bdim 12593 through ax-bdsb 12601) can be written either in closed or inference form. The fact that ax-bd0 12592 is an inference is enough to ensure that the closed forms cannot be "exploited" to prove that some unbounded formulas are bounded. (TODO: check.) However, we state all the axioms in inference form to make it clear that we do not exploit any over-permissiveness. Finally, note that our logic has no terms, only variables. Therefore, we cannot prove for instance that is a bounded formula. However, since can be defined as "the such that PHI" a proof using the fact that is bounded can be converted to a proof in iset.mm by replacing with everywhere and prepending the antecedent PHI, since is bounded by ax-bdel 12600. For a similar method, see bj-omtrans 12739. Note that one cannot add an axiom BOUNDED since by bdph 12629 it would imply that every formula is bounded. | ||||||||||||||||||||||||||
Syntax | wbd 12591 | Syntax for the predicate BOUNDED. | ||||||||||||||||||||||||
BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bd0 12592 | If two formulas are equivalent, then boundedness of one implies boundedness of the other. (Contributed by BJ, 3-Oct-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdim 12593 | An implication between two bounded formulas is bounded. (Contributed by BJ, 25-Sep-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdan 12594 | The conjunction of two bounded formulas is bounded. (Contributed by BJ, 25-Sep-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdor 12595 | The disjunction of two bounded formulas is bounded. (Contributed by BJ, 25-Sep-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdn 12596 | The negation of a bounded formula is bounded. (Contributed by BJ, 25-Sep-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdal 12597* | A bounded universal quantification of a bounded formula is bounded. Note the disjoint variable condition on . (Contributed by BJ, 25-Sep-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdex 12598* | A bounded existential quantification of a bounded formula is bounded. Note the disjoint variable condition on . (Contributed by BJ, 25-Sep-2019.) | ||||||||||||||||||||||||
BOUNDED BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdeq 12599 | An atomic formula is bounded (equality predicate). (Contributed by BJ, 3-Oct-2019.) | ||||||||||||||||||||||||
BOUNDED | ||||||||||||||||||||||||||
Axiom | ax-bdel 12600 | An atomic formula is bounded (membership predicate). (Contributed by BJ, 3-Oct-2019.) | ||||||||||||||||||||||||
BOUNDED |
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