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Type | Label | Description | ||||||||||||||
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Statement | ||||||||||||||||

Theorem | con5 27301 | Bi-conditional contraposition variation. This proof is con5VD 27689 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | con5i 27302 | Inference form of con5 27301. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | exlimexi 27303 | Inference similar to Theorem 19.23 of [Margaris] p. 90. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | sb5ALT 27304* | Equivalence for substitution. Alternate proof of sb5 1994. This proof is sb5ALTVD 27702 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | eexinst01 27305 | exinst01 27410 without virtual deductions. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | eexinst11 27306 | exinst11 27411 without virtual deductions. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vk15.4j 27307 | Excercise 4j of Unit 15 of "Understanding Symbolic Logic", Fifth Edition (2008), by Virginia Klenk. This proof is the minimized Hilbert-style axiomatic version of the Fitch-style Natural Deduction proof found on page 442 of Klenk and was automatically derived from that proof. vk15.4j 27307 is vk15.4jVD 27703 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | notnot2ALT 27308 | Converse of double negation. Alternate proof of notnot2 106. This proof is notnot2ALTVD 27704 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | con3ALT 27309 | Contraposition. Alternate proof of con3 128. This proof is con3ALTVD 27705 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | ssralv2 27310* |
Quantification restricted to a subclass for two quantifiers. ssralv 3179
for two quantifiers. The proof of ssralv2 27310 was automatically generated
by minimizing the automatically translated proof of ssralv2VD 27655. The
automatic translation is by the tools program
translate_{without}_overwriting.cmd
(Contributed by Alan Sare,
18-Feb-2012.) (Proof modification is discouraged.)
(New usage is discouraged.)
| ||||||||||||||

Theorem | sbc3org 27311 | sbcorg 2980 with a 3-disjuncts. This proof is sbc3orgVD 27640 automatically translated and minimized. (Contributed by Alan Sare, 31-Dec-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | alrim3con13v 27312* | Closed form of alrimi 1706 with 2 additional conjuncts having no occurences of the quantifying variable. This proof is 19.21a3con13vVD 27641 automatically translated and minimized. (Contributed by Alan Sare, 31-Dec-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | ra4sbc2 27313* | ra4sbc 3013 with two quantifying variables. This proof is ra4sbc2VD 27644 automatically translated and minimized. (Contributed by Alan Sare, 31-Dec-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | sbcoreleleq 27314* | Substitution of a set variable for another set variable in a 3-conjunct formula. Derived automatically from sbcoreleleqVD 27648. (Contributed by Alan Sare, 31-Dec-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | tratrb 27315* | If a class is transitive and any two distinct elements of the class are E-comparable, then every element of that class is transitive. Derived automatically from tratrbVD 27650. (Contributed by Alan Sare, 31-Dec-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 3ax5 27316 | ax-5 1533 for a 3 element left-nested implication. Derived automatically from 3ax5VD 27651. (Contributed by Alan Sare, 31-Dec-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | ordelordALT 27317 | An element of an ordinal class is ordinal. Proposition 7.6 of [TakeutiZaring] p. 36. This is an alternate proof of ordelord 4351 using the Axiom of Regularity indirectly through dford2 7254. dford2 is a weaker definition of ordinal number. Given the Axiom of Regularity, it need not be assumed that because this is inferred by the Axiom of Regularity. ordelordALT 27317 is ordelordALTVD 27656 without virtual deductions and was automatically derived from ordelordALTVD 27656 using the tools program translate..without..overwriting.cmd and Metamath's minimize command. (Contributed by Alan Sare, 18-Feb-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | sbcim2g 27318 | Distribution of class substitution over a left-nested implication. Similar to sbcimg 2976. sbcim2g 27318 is sbcim2gVD 27664 without virtual deductions and was automatically derived from sbcim2gVD 27664 using the tools program translate..without..overwriting.cmd and Metamath's minimize command. (Contributed by Alan Sare, 18-Mar-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | sbcbi 27319 | Implication form of sbcbiiOLD 2991. sbcbi 27319 is sbcbiVD 27665 without virtual deductions and was automatically derived from sbcbiVD 27665 using the tools program translate..without..overwriting.cmd and Metamath's minimize command. (Contributed by Alan Sare, 18-Mar-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | trsbc 27320* | Formula-building inference rule for class substitution, substituting a class variable for the set variable of the transitivity predicate. trsbc 27320 is trsbcVD 27666 without virtual deductions and was automatically derived from trsbcVD 27666 using the tools program translate..without..overwriting.cmd and Metamath's minimize command. (Contributed by Alan Sare, 18-Mar-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | truniALT 27321* | The union of a class of transitive sets is transitive. Alternate proof of truni 4067. truniALT 27321 is truniALTVD 27667 without virtual deductions and was automatically derived from truniALTVD 27667 using the tools program translate..without..overwriting.cmd and Metamath's minimize command. (Contributed by Alan Sare, 18-Mar-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | sbcss 27322 | Distribute proper substitution through a subclass relation. This theorem was automatically derived from sbcssVD 27672. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | onfrALTlem5 27323* | Lemma for onfrALT 27330. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | onfrALTlem4 27324* | Lemma for onfrALT 27330. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | onfrALTlem3 27325* | Lemma for onfrALT 27330. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | ggen31 27326* | gen31 27406 without virtual deductions. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | onfrALTlem2 27327* | |||||||||||||||

Theorem | cbvexsv 27328* | A theorem pertaining to the substitution for an existentially quantified variable when the substituted variable does not occur in the quantified wff. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | onfrALTlem1 27329* | |||||||||||||||

Theorem | onfrALT 27330 | The epsilon relation is foundational on the class of ordinal numbers. onfrALT 27330 is an alternate proof of onfr 4368. onfrALTVD 27680 is the Virtual Deduction proof from which onfrALT 27330 is derived. The Virtual Deduction proof mirrors the working proof of onfr 4368 which is the main part of the proof of Theorem 7.12 of the first edition of TakeutiZaring. The proof of the corresponding Proposition 7.12 of [TakeutiZaring] p. 38 (second edition) does not contain the working proof equivalent of onfrALTVD 27680. This theorem does not rely on the Axiom of Regularity. (Contributed by Alan Sare, 22-Jul-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | csbeq2g 27331 | Formula-building implication rule for class substitution. Closed form of csbeq2i 3049. csbeq2g 27331 is derived from the virtual deduction proof csbeq2gVD 27681. (Contributed by Alan Sare, 10-Nov-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 19.41rg 27332 | Closed form of right-to-left implication of 19.41 1799, Theorem 19.41 of [Margaris] p. 90. Derived from 19.41rgVD 27691. (Contributed by Alan Sare, 8-Feb-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | opelopab4 27333* | Ordered pair membership in a class abstraction of pairs. Compare to elopab 4209. (Contributed by Alan Sare, 8-Feb-2014.) (Revised by Mario Carneiro, 6-May-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 2pm13.193 27334 | pm13.193 26944 for two variables. pm13.193 26944 is Theorem *13.193 in [WhiteheadRussell] p. 179. Derived from 2pm13.193VD 27692. (Contributed by Alan Sare, 8-Feb-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | hbntal 27335 | A closed form of hbn 1722. hbnt 1717 is another closed form of hbn 1722. (Contributed by Alan Sare, 8-Feb-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | hbimpg 27336 | A closed form of hbim 1723. Derived from hbimpgVD 27693. (Contributed by Alan Sare, 8-Feb-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | hbalg 27337 | Closed form of hbal 1567. Derived from hbalgVD 27694. (Contributed by Alan Sare, 8-Feb-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | hbexg 27338 | Closed form of nfex 1733. Derived from hbexgVD 27695. (Contributed by Alan Sare, 8-Feb-2014.) (Revised by Mario Carneiro, 12-Dec-2016.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | a9e2eq 27339* | Alternate form of a9e 1817 for non-distinct , and . a9e2eq 27339 is derived from a9e2eqVD 27696. (Contributed by Alan Sare, 25-Mar-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | a9e2nd 27340* | If at least two sets exist (dtru 4139) , then the same is true expressed in an alternate form similar to the form of a9e 1817. a9e2nd 27340 is derived from a9e2ndVD 27697. (Contributed by Alan Sare, 25-Mar-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | a9e2ndeq 27341* | "At least two sets exist" expressed in the form of dtru 4139 is logically equivalent to the same expressed in a form similar to a9e 1817 if dtru 4139 is false implies . a9e2ndeq 27341 is derived from a9e2ndeqVD 27698. (Contributed by Alan Sare, 25-Mar-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 2sb5nd 27342* | Equivalence for double substitution 2sb5 2075 without distinct , requirement. 2sb5nd 27342 is derived from 2sb5ndVD 27699. (Contributed by Alan Sare, 30-Apr-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 2uasbanh 27343* | Distribute the unabbreviated form of proper substitution in and out of a conjunction. 2uasbanh 27343 is derived from 2uasbanhVD 27700. (Contributed by Alan Sare, 31-May-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 2uasban 27344* | Distribute the unabbreviated form of proper substitution in and out of a conjunction. (Contributed by Alan Sare, 31-May-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | e2ebind 27345 | Absorption of an existential quantifier of a double existential quantifier of non-distinct variables. e2ebind 27345 is derived from e2ebindVD 27701. (Contributed by Alan Sare, 27-Nov-2014.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | elpwgded 27346 | elpwgdedVD 27706 in conventional notation. (Contributed by Alan Sare, 23-Apr-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | trelded 27347 | Deduction form of trel 4060. In a transitive class, the membership relation is transitive. (Contributed by Alan Sare, 3-Dec-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | jaoded 27348 | Deduction form of jao 500. Disjunction of antecedents. (Contributed by Alan Sare, 3-Dec-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | 3imp31 27349 | The importation inference 3imp 1150 with commutation of the first and third conjuncts of the assertion relative to the hypothesis. (Contributed by Alan Sare, 11-Sep-2016.) (Proof modification is discouraged.) | ||||||||||||||

Theorem | 3imp21 27350 | The importation inference 3imp 1150 with commutation of the first and second conjuncts of the assertion relative to the hypothesis. (Contributed by Alan Sare, 11-Sep-2016.) (Proof modification is discouraged.) | ||||||||||||||

Theorem | biimpa21 27351 | biimpa 472 with commutation of the first and second conjuncts of the assertion. (Contributed by Alan Sare, 11-Sep-2016.) | ||||||||||||||

Theorem | sbtT 27352 | A substitution into a theorem remains true. sbt 1906 with the existence of no virtual hypotheses for the hypothesis expressed as the empty virtual hypothesis collection. (Contributed by Alan Sare, 4-Feb-2017.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

16.22.2 What is Virtual Deduction? | ||||||||||||||||

Syntax | wvd1 27353 |
A Virtual Deduction proof in a Hilbert-style deductive system is the
analog of a sequent calculus proof. A theorem is proven in a Gentzen
system in order to prove more directly, which may be more intuitive
and easier for some people. The analog of this proof in Metamath's
Hilbert-style system is verified by the Metamath program.
Natural Deduction is a well known proof method orignally proposed by Gentzen in 1935 and comprehensively summarized by Prawitz in his 1965 monograph "Natural deduction: a proof-theoretic study". Gentzen wished to construct "a formalism that comes as close as possible to natural reasoning". Natural deduction is a response to dissatisfaction with axiomatic proofs such as Hilbert-style axiomatic proofs, which the proofs of Metamath are. In 1926, in Poland, Lukasiewicz advocated a more natural treatment of logic. Jaskowski made the earliest attempts at defining a more natural deduction. Natural deduction in its modern form was independently proposed by Gentzen. Sequent calculus, the chief alternative to Natural Deduction, was created by Gentzen. The following is an except from Stephen Cole Kleene's seminal 1952 book "Introduction to Metamathematics", which contains the first formulation of sequent calculus in the modern style. Kleene states on page 440: . . . the proof of (Gentzen's Hauptsatz) breaks down into a list of cases, each of which is simple to handle. . . . Gentzen's normal form for proofs in the predicate calculus requires a different classification of the deductive steps than is given by the postulates of the formal system of predicate calculus of Chapter IV (Section 19). The implication symbol (the Metamath symbol for implication has been substituted here for the symbol used by Kleene) has to be separated in its role of mediating inferences from its role as a component symbol of the formula being proved. In the former role it will be replaced by a new formal symbol (read "gives" or "entails"), to which properties will be assigned similar to those of the informal symbol in our former derived rules. Gentzen's classification of the deductive operations is made explicit by setting up a new formal system of the predicate calculus. The formal system of propositional and predicate calculus studied previously (Chapters IV ff.) we call now a "Hilbert-type system", and denote by H. Precisely, H denotes any one or a particular one of several systems, according to whether we are considering propositional calculus or predicate calculus, in the classical or the intuitionistic version (Section 23), and according to the sense in which we are using "term" and "formula" (Sections 117,25,31,37,72-76). The same respective choices will apply to the "Gentzen-type system G1" which we introduce now and the G2, G3 and G3a later. The transformation or deductive rules of G1 will apply to objects which are not formulas of the system H, but are built from them by an additional formation rule, so we use a new term "sequent" for these objects. (Gentzen says "Sequenz", which we translate as "sequent", because we have already used "sequence" for any succession of objects, where the German is "Folge".) A sequent is a formal expression of the form , . . . , , . . . , where , . . . , and , . . . , are seqences of a finite number of 0 or more formulas (substituting Metamath notation for Kleene's notation). The part , . . . , is the antecedent, and , . . . , the succedent of the sequent , . . . , , . . . , . When the antecedent and the succedent each have a finite number of 1 or more formulas, the sequent , . . . , , . . . has the same interpretation for G1 as the formula . . . . . . for H. The interpretation extends to the case of an antecedent of 0 formulas by regarding . . . for 0 formulas (the "empty conjunction") as true and . . . for 0 formulas (the "empty disjunction") as false. . . . As in Chapter V, we use Greek capitals . . . to stand for finite sequences of zero or more formulas, but now also as antecedent (succedent), or parts of antecedent (succedent), with separating formal commas included. . . . (End of Kleene excerpt) In chapter V entitled "Formal Deduction" Kleene states, on page 86: Section 20. Formal deduction. Formal proofs of even quite elementary theorems tend to be long. As a price for having analyzed logical deduction into simple steps, more of those steps have to be used. The purpose of formalizing a theory is to get an explicit definition of what constitutes proof in the theory. Having achieved this, there is no need always to appeal directly to the definition. The labor required to establish the formal provability of formulas can be greatly lessened by using metamathematical theorems concerning the existence of formal proofs. If the demonstrations of those theorems do have the finitary character which metamathematics is supposed to have, the demonstrations will indicate, at least implicitly, methods for obtaining the formal proofs. The use of the metamathematical theorems then amounts to abbreviation, often of very great extent, in the presentation of formal proofs. The simpler of such metamathematical theorems we shall call derived rules, since they express principles which can be said to be derived from the postulated rules by showing that the use of them as additional methods of inference does not increase the class of provable formulas. We shall seek by means of derived rules to bring the methods for establishing the facts of formal provability as close as possible to the informal methods of the theory which is being formalized. In setting up the formal system, proof was given the simplest possible structure, consisting of a single sequence of formulas. Some of our derived rules, called "direct rules", will serve to abbreviate for us whole segments of such a sequence; we can then, so to speak, use these segments as prefabricated units in building proofs. But also, in mathematical practice, proofs are common which have a more complicated structure, employing "subsidiary deduction", i.e. deduction under assumptions for the sake of the argument, which assumptions are subsequently discharged. For example, subsidiary deduction is used in a proof by reductio ad absurdum, and less obtrusively when we place the hypothesis of a theorem on a par with proved propositions to deduce the conclusion. Other derived rules, called "subsidiary deduction rules", will give us this kind of procedure. We now introduce, by a metamathematical definition, the notion of "formal deducibility under assumptions". Given a list , . . . of or more (occurences of) formulas, a finite sequence of one or more (occurences of) formulas is called a (formal) deduction from the assumption formulas , . . . , if each formula of the sequence is either one of the formulas , . . . , or an axiom, or an immediate consequence of preceding formulas of a sequence. A deduction is said to be deducible from the assumption formulas (in symbols, ,. . . . ,. ), and is called the conclusion (or endformula) of the deduction. (The symbol may be read "yields".) (End of Kleene excerpt) Gentzen's normal form is a certain direct fashion for proofs and deductions. His sequent calculus, formulated in the modern style by Kleene, is the classical system G1. In this system, the new formal symbol has properties similar to the informal symbol of Kleene's above language of formal deducibility under assumptions. Kleene states on page 440: . . . This leads us to inquire whether there may not be a theorem about the predicate calculus asserting that, if a formula is provable (or deducible from other formulas), it is provable (or deducible) in a certain direct fashion; in other words, a theorem giving a normal form for proofs and deductions, the proofs and deduction in normal form being in some sense direct. (End of Kleene excerpt) There is such a theorem, which was proven by Kleene. Formal proofs in H of even quite elementary theorems tend to be long. As a price for having analyzed logical deduction into simple steps, more of those steps have to be used. The proofs of Metamath are fully detailed formal proofs. We wish to have a means of proving Metamath theorems and deductions in a more direct fashion. Natural Deduction is a system for proving theorems and deductions in a more direct fashion. However, Natural Deduction is not compatible for use with Metamath, which uses a Hilbert-type system. Instead, Kleene's classical system G1 may be used for proving Metamath deductions and theorems in a more direct fashion. The system of Metamath is an H system, not a Gentzen system. Therefore, proofs in Kleene's classical system G1 ("G1") cannot be included in Metamath's system H, which we shall henceforth call "system H" or "H". However, we may translate proofs in G1 into proofs in H. By Kleene's THEOREM 47 (page 446)
By Kleene's COROLLARY of THEOREM 47 (page 448)
denotes the same connective denoted by . " , " , in the context of Virtual Deduction, denotes the same connective denoted by . This Virtual Deduction notation is specified by the following set.mm definitions:
replaces in the analog in H of a sequent in G1 having a non-empty antecedent. If occurs as the outermost connective denoted by or and occurs exactly once, we call the analog in H of a sequent in G1 a "virtual deduction" because the corresponding of the sequent is assigned properties similar to . While sequent calculus proofs (proofs in G1) may have as steps sequents with 0, 1, or more formulas in the succedent, we shall only prove in G1 using sequents with exactly 1 formula in the succedent. The User proves in G1 in order to obtain the benefits of more direct proving using sequent calculus, then translates the proof in G1 into a proof in H. The reference theorems and deductions to be used for proving in G1 are translations of theorems and deductions in set.mm. Each theorem in set.mm corresponds to the theorem in G1. Deductions in G1 corresponding to deductions in H are similarly determined. Theorems in H with one or more occurences of either or may also be translated into theorems in G1 for by replacing the outermost occurence of or of the theorem in H with . Deductions in H may be translated into deductions in G1 in a similar manner. The only theorems and deductions in H useful for proving in G1 for the purpose of obtaining proofs in H are those in which, for each hypothesis or assertion, there are 0 or 1 occurences of and it is the outermost occurence of or . Kleene's THEOREM 46 and its COROLLARY 2 are used for translating from H to G1. By Kleene's THEOREM 46 (page 445)
By Kleene's COROLLARY 2 of THEOREM 46 (page 446)
The procedure for more direct proving of theorems or deductions in H is as follows. The User proves in G1. He(she) uses translated set.mm theorems and deductions as reference theorems and deductions. His(her) proof is only a guess in the sense that he(she) can't verify his(her) proof in G1 because he(she) doesn't have an automated proof checker to use. The proof in G1 is translated into its analog in H for verification by the Metamath program. This proof is called the Virtual Deduction proof. This proof may then be translated into a conventional Metamath proof automatically, removing the unnecessary Virtual Deduction symbols. The translations from H to G1 and G1 to H are trivial. In practice, they may be done without much thought. In principle, they must be done, because the proving is done using sequents, which do not exist in H. The analogs in H of the postulates of G1 are the set.mm postulates. The postulates in G1 corresponding to the Metamath postulates are not the classical system G1 postulates of Kleene (pages 442 and 443). set.mm has the predicate calculus postulates and other posulates. The Kleene classical system G1 postulates correspond to predicate calculus postulates which differ from the Metamath system G1 postulates corresponding to the predicate calculus postulates of Metamath's system H. Metamath's predicate calculus G1 postulates are presumably deducible from the Kleene classical G1 postulates and the Kleene classical G1 postulates are deducible from Metamath's G1 postulates. It should be recognized that, because of the different postulates, the classical G1 system corresponding to Metamath's system H is not identical to Kleene's classical system G1.
Why not create a separate database (setg.mm) of proofs in G1, avoiding the need to translate from H to G1 and from G1 back to H? The translations are trivial. Sequents make the language more complex than is necessary. More direct proving using sequent calculus may be done as a means towards the end of constructing proofs in H. Then, the language may be kept as simple as possible. A system G1 database would be redundant because it would duplicate the information contained in the corresponding system H database. For earlier proofs, each "User's Proof" in the web page description of a Virtual Deduction proof in set.mm is the analog in H of the User's working proof in G1. The User's Proof is automatically completed by completeusersproof.cmd. The completed proof is the Virtual Deduction proof, which is the analog in H of the corresponding fully detailed proof in G1. The completed Virtual Deduction proof of these earlier proofs may be automatically translated into a conventional Metamath proof. In September of 2016 completeusersproof.c was released. The input for completeusersproof.c is a Virtual Deduction User's Proof. Unlike completeusersproof.cmd, the completed proof is in conventional notation. completeusersproof.c eliminates the virtual deduction notation of the User's Proof after utilizing the information it provides. Applying mmj2's unify command is essential to completeusersproof.c. The mmj2 program is invoked within the completeusersproof.c function mmj2Unify(). The original mmj2 program was written by Mel O'Cat. Mario Carneiro has enhanced it. mmj2Unify() is called multiple times during the execution of completeusersproof. A Virtual Deduction proof is the Metamath-specific version of a Natural Deduction Proof. A Virtual Deduction proof generally cannot be directly input on a mmj2 Proof Worksheet and completed by the mmj2 tool because it is usually missing some technical proof steps which are not part of the Virtual Deduction proof but are necessary for a complete Metamath Proof. These missing technical steps may be automatically added by an automated proof assistant. completeusersproof.c is such a proof assistant. completeusersproof.c adds the missing technical steps and finds the reference theorems and deductions in set.mm which unify with the subproofs of the proof. The User may write a Virtual Deduction proof and automatically transform it into a complete Metamath proof using the completeusersproof tool. The completed proof has been checked by the Metamath program. The task of writing a complete Metamath proof is reduced to writing what is essentially a Natural Deduction Proof. Generally, proving using Virtual Deduction and completeusersproof reduces the amount Metamath-specific knowledge required by the User. Often, no knowledge of the specific theorems and deductions in set.mm is required to write some of the subproofs of a Virtual Deduction proof. Often, no knowledge of the Metamath-specific names of reference theorems and deductions in set.mm is required for writing some of the subproofs of a User's Proof. Often, the User may write subproofs of a proof using theorems or deductions commonly used in mathematics and correctly assume that some form of each is contained in set.mm and that completeusersproof will automatically generate the technical steps necessary to utilize them to complete the subproofs. Often, the fraction of the work which may be considered tedious is reduced and the total amount of work is reduced. | ||||||||||||||

16.22.3 Virtual Deduction Theorems | ||||||||||||||||

Definition | df-vd1 27354 | Definition of virtual deduction. (Contributed by Alan Sare, 21-Apr-2011.) (New usage is discouraged.) | ||||||||||||||

Theorem | in1 27355 | Inference form of df-vd1 27354. Virtual deduction introduction rule of converting the virtual hypothesis of a 1-virtual hypothesis virtual deduction into an antecedent. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | iin1 27356 | in1 27355 without virtual deductions. (Contributed by Alan Sare, 23-Jul-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd1ir 27357 | Inference form of df-vd1 27354 with the virtual deduction as the assertion. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | idn1 27358 | Virtual deduction identity rule which is id 21 with virtual deduction symbols. (Contributed by Alan Sare, 24-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | ax172 27359* | Quantification of two variables over a formula in which they do not occur. (Contributed by Alan Sare, 12-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd1imp 27360 | Left-to-right part of definition of virtual deduction. (Contributed by Alan Sare, 21-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd1impr 27361 | Right-to-left part of definition of virtual deduction. (Contributed by Alan Sare, 21-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Syntax | wvd2 27362 | Syntax for a 2-hypothesis virtual deduction. (New usage is discouraged.) | ||||||||||||||

Definition | df-vd2 27363 | Definition of a 2-hypothesis virtual deduction. (Contributed by Alan Sare, 14-Nov-2011.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2 27364 | Definition of a 2-hypothesis virtual deduction. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Syntax | wvhc2 27365 | Syntax for a 2-virtual hypotheses collection. (Contributed by Alan Sare, 23-Apr-2015.) (New usage is discouraged.) | ||||||||||||||

Definition | df-vhc2 27366 | Definition of a 2-virtual hypotheses collection. (Contributed by Alan Sare, 23-Apr-2015.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2an 27367 | Definition of a 2-hypothesis virtual deduction in vd conjunction form. (Contributed by Alan Sare, 23-Apr-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2ani 27368 | Inference form of dfvd2an 27367. (Contributed by Alan Sare, 23-Apr-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2anir 27369 | Right-to-left inference form of dfvd2an 27367. (Contributed by Alan Sare, 23-Apr-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2i 27370 | Inference form of dfvd2 27364. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2ir 27371 | Right-to-left inference form of dfvd2 27364. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Syntax | wvd3 27372 | Syntax for a 3-hypothesis virtual deduction. (New usage is discouraged.) | ||||||||||||||

Syntax | wvhc3 27373 | Syntax for a 3-virtual hypotheses collection. (Contributed by Alan Sare, 13-Jun-2015.) (New usage is discouraged.) | ||||||||||||||

Definition | df-vhc3 27374 | Definition of a 3-virtual hypotheses collection. (Contributed by Alan Sare, 13-Jun-2015.) (New usage is discouraged.) | ||||||||||||||

Definition | df-vd3 27375 | Definition of a 3-hypothesis virtual deduction. (Contributed by Alan Sare, 14-Nov-2011.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd3 27376 | Definition of a 3-hypothesis virtual deduction. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd3i 27377 | Inference form of dfvd3 27376. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd3ir 27378 | Right-to-left inference form of dfvd3 27376. (Contributed by Alan Sare, 14-Nov-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd3an 27379 | Definition of a 3-hypothesis virtual deduction in vd conjunction form. (Contributed by Alan Sare, 13-Jun-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd3ani 27380 | Inference form of dfvd3an 27379. (Contributed by Alan Sare, 13-Jun-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd3anir 27381 | Right-to-left inference form of dfvd3an 27379. (Contributed by Alan Sare, 13-Jun-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vd01 27382 | A virtual hypothesis virtually infers a theorem. (Contributed by Alan Sare, 14-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vd02 27383 | 2 virtual hypotheses virtually infer a theorem. (Contributed by Alan Sare, 14-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vd03 27384 | A theorem is virtually inferred by the 3 virtual hypotheses. (Contributed by Alan Sare, 12-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vd12 27385 | A virtual deduction with 1 virtual hypothesis virtually inferring a virtual conclusion infers that the same conclusion is virtually inferred by the same virtual hypothesis and an additional hypothesis. (Contributed by Alan Sare, 12-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vd13 27386 | A virtual deduction with 1 virtual hypothesis virtually inferring a virtual conclusion infers that the same conclusion is virtually inferred by the same virtual hypothesis and a two additional hypotheses. (Contributed by Alan Sare, 12-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | vd23 27387 | A virtual deduction with 2 virtual hypotheses virtually inferring a virtual conclusion infers that the same conclusion is virtually inferred by the same 2 virtual hypotheses and a third hypothesis. (Contributed by Alan Sare, 12-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2imp 27388 | The virtual deduction form of a 2-antecedent nested implication implies the 2-antecedent nested implication. (Contributed by Alan Sare, 21-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | dfvd2impr 27389 | A 2-antecedent nested implication implies its virtual deduction form. (Contributed by Alan Sare, 21-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | in2 27390 | The virtual deduction introduction rule of converting the end virtual hypothesis of 2 virtual hypotheses into an antecedent. (Contributed by Alan Sare, 21-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | int2 27391 | The virtual deduction introduction rule of converting the end virtual hypothesis of 2 virtual hypotheses into an antecedent. Conventional form of int2 27391 is ex 425. (Contributed by Alan Sare, 23-Apr-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | iin2 27392 | in2 27390 without virtual deductions. (Contributed by Alan Sare, 20-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | in2an 27393 | The virtual deduction introduction rule converting the second conjunct of the second virtual hypothesis into the antecedent of the conclusion. exp3a 427 is the non-virtual deduction form of in2an 27393. (Contributed by Alan Sare, 30-Jun-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | in3 27394 | The virtual deduction introduction rule of converting the end virtual hypothesis of 3 virtual hypotheses into an antecedent. (Contributed by Alan Sare, 12-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | iin3 27395 | in3 27394 without virtual deduction connectives. Special theorem needed for Alan Sare's virtual deduction translation tool. (Contributed by Alan Sare, 23-Jul-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | in3an 27396 | The virtual deduction introduction rule converting the second conjunct of the third virtual hypothesis into the antecedent of the conclusion. exp4a 592 is the non-virtual deduction form of in3an 27396. (Contributed by Alan Sare, 25-Jun-2012.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | int3 27397 | The virtual deduction introduction rule of converting the end virtual hypothesis of 3 virtual hypotheses into an antecedent. Conventional form of int3 27397 is 3expia 1158. (Contributed by Alan Sare, 13-Jun-2015.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | idn2 27398 | Virtual deduction identity rule which is idd 23 with virtual deduction symbols. (Contributed by Alan Sare, 21-Apr-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | iden2 27399 | Virtual deduction identity rule. simpr 449 in conjunction form Virtual Deduction notation. (Contributed by Alan Sare, 5-Sep-2016.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

Theorem | idn3 27400 | Virtual deduction identity rule for 3 virtual hypotheses. (Contributed by Alan Sare, 11-Jun-2011.) (Proof modification is discouraged.) (New usage is discouraged.) | ||||||||||||||

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