P. 14 of Theorem List - Intuitionistic Logic Explorer

Theorem List for Intuitionistic Logic Explorer - 1301-1400   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	syl3anr1 1301	A syllogism inference. (Contributed by NM, 31-Jul-2007.)
|- ( ph -> ps )   &    |- ( ( ch /\ ( ps /\ th /\ ta ) ) -> et )   =>    |- ( ( ch /\ ( ph /\ th /\ ta ) ) -> et )
Theorem	syl3anr2 1302	A syllogism inference. (Contributed by NM, 1-Aug-2007.)
|- ( ph -> th )   &    |- ( ( ch /\ ( ps /\ th /\ ta ) ) -> et )   =>    |- ( ( ch /\ ( ps /\ ph /\ ta ) ) -> et )
Theorem	syl3anr3 1303	A syllogism inference. (Contributed by NM, 23-Aug-2007.)
|- ( ph -> ta )   &    |- ( ( ch /\ ( ps /\ th /\ ta ) ) -> et )   =>    |- ( ( ch /\ ( ps /\ th /\ ph ) ) -> et )
Theorem	syldbl2 1304	Stacked hypotheseis implies goal. (Contributed by Stanislas Polu, 9-Mar-2020.)
|- ( ( ph /\ ps ) -> ( ps -> th ) )   =>    |- ( ( ph /\ ps ) -> th )
Theorem	3impdi 1305	Importation inference (undistribute conjunction). (Contributed by NM, 14-Aug-1995.)
|- ( ( ( ph /\ ps ) /\ ( ph /\ ch ) ) -> th )   =>    |- ( ( ph /\ ps /\ ch ) -> th )
Theorem	3impdir 1306	Importation inference (undistribute conjunction). (Contributed by NM, 20-Aug-1995.)
|- ( ( ( ph /\ ps ) /\ ( ch /\ ps ) ) -> th )   =>    |- ( ( ph /\ ch /\ ps ) -> th )
Theorem	3anidm12 1307	Inference from idempotent law for conjunction. (Contributed by NM, 7-Mar-2008.)
|- ( ( ph /\ ph /\ ps ) -> ch )   =>    |- ( ( ph /\ ps ) -> ch )
Theorem	3anidm13 1308	Inference from idempotent law for conjunction. (Contributed by NM, 7-Mar-2008.)
|- ( ( ph /\ ps /\ ph ) -> ch )   =>    |- ( ( ph /\ ps ) -> ch )
Theorem	3anidm23 1309	Inference from idempotent law for conjunction. (Contributed by NM, 1-Feb-2007.)
|- ( ( ph /\ ps /\ ps ) -> ch )   =>    |- ( ( ph /\ ps ) -> ch )
Theorem	syl2an3an 1310	syl3an 1291 with antecedents in standard conjunction form. (Contributed by Alan Sare, 31-Aug-2016.)
|- ( ph -> ps )   &    |- ( ph -> ch )   &    |- ( th -> ta )   &    |- ( ( ps /\ ch /\ ta ) -> et )   =>    |- ( ( ph /\ th ) -> et )
Theorem	syl2an23an 1311	Deduction related to syl3an 1291 with antecedents in standard conjunction form. (Contributed by Alan Sare, 31-Aug-2016.)
|- ( ph -> ps )   &    |- ( ph -> ch )   &    |- ( ( th /\ ph ) -> ta )   &    |- ( ( ps /\ ch /\ ta ) -> et )   =>    |- ( ( th /\ ph ) -> et )
Theorem	3ori 1312	Infer implication from triple disjunction. (Contributed by NM, 26-Sep-2006.)
|- ( ph \/ ps \/ ch )   =>    |- ( ( -. ph /\ -. ps ) -> ch )
Theorem	3jao 1313	Disjunction of 3 antecedents. (Contributed by NM, 8-Apr-1994.)
|- ( ( ( ph -> ps ) /\ ( ch -> ps ) /\ ( th -> ps ) ) -> ( ( ph \/ ch \/ th ) -> ps ) )
Theorem	3jaob 1314	Disjunction of 3 antecedents. (Contributed by NM, 13-Sep-2011.)
|- ( ( ( ph \/ ch \/ th ) -> ps ) <-> ( ( ph -> ps ) /\ ( ch -> ps ) /\ ( th -> ps ) ) )
Theorem	3jaoi 1315	Disjunction of 3 antecedents (inference). (Contributed by NM, 12-Sep-1995.)
|- ( ph -> ps )   &    |- ( ch -> ps )   &    |- ( th -> ps )   =>    |- ( ( ph \/ ch \/ th ) -> ps )
Theorem	3jaod 1316	Disjunction of 3 antecedents (deduction). (Contributed by NM, 14-Oct-2005.)
|- ( ph -> ( ps -> ch ) )   &    |- ( ph -> ( th -> ch ) )   &    |- ( ph -> ( ta -> ch ) )   =>    |- ( ph -> ( ( ps \/ th \/ ta ) -> ch ) )
Theorem	3jaoian 1317	Disjunction of 3 antecedents (inference). (Contributed by NM, 14-Oct-2005.)
|- ( ( ph /\ ps ) -> ch )   &    |- ( ( th /\ ps ) -> ch )   &    |- ( ( ta /\ ps ) -> ch )   =>    |- ( ( ( ph \/ th \/ ta ) /\ ps ) -> ch )
Theorem	3jaodan 1318	Disjunction of 3 antecedents (deduction). (Contributed by NM, 14-Oct-2005.)
|- ( ( ph /\ ps ) -> ch )   &    |- ( ( ph /\ th ) -> ch )   &    |- ( ( ph /\ ta ) -> ch )   =>    |- ( ( ph /\ ( ps \/ th \/ ta ) ) -> ch )
Theorem	mpjao3dan 1319	Eliminate a 3-way disjunction in a deduction. (Contributed by Thierry Arnoux, 13-Apr-2018.)
|- ( ( ph /\ ps ) -> ch )   &    |- ( ( ph /\ th ) -> ch )   &    |- ( ( ph /\ ta ) -> ch )   &    |- ( ph -> ( ps \/ th \/ ta ) )   =>    |- ( ph -> ch )
Theorem	3jaao 1320	Inference conjoining and disjoining the antecedents of three implications. (Contributed by Jeff Hankins, 15-Aug-2009.) (Proof shortened by Andrew Salmon, 13-May-2011.)
|- ( ph -> ( ps -> ch ) )   &    |- ( th -> ( ta -> ch ) )   &    |- ( et -> ( ze -> ch ) )   =>    |- ( ( ph /\ th /\ et ) -> ( ( ps \/ ta \/ ze ) -> ch ) )
Theorem	3ianorr 1321	Triple disjunction implies negated triple conjunction. (Contributed by Jim Kingdon, 23-Dec-2018.)
|- ( ( -. ph \/ -. ps \/ -. ch ) -> -. ( ph /\ ps /\ ch ) )
Theorem	syl3an9b 1322	Nested syllogism inference conjoining 3 dissimilar antecedents. (Contributed by NM, 1-May-1995.)
|- ( ph -> ( ps <-> ch ) )   &    |- ( th -> ( ch <-> ta ) )   &    |- ( et -> ( ta <-> ze ) )   =>    |- ( ( ph /\ th /\ et ) -> ( ps <-> ze ) )
Theorem	3orbi123d 1323	Deduction joining 3 equivalences to form equivalence of disjunctions. (Contributed by NM, 20-Apr-1994.)
|- ( ph -> ( ps <-> ch ) )   &    |- ( ph -> ( th <-> ta ) )   &    |- ( ph -> ( et <-> ze ) )   =>    |- ( ph -> ( ( ps \/ th \/ et ) <-> ( ch \/ ta \/ ze ) ) )
Theorem	3anbi123d 1324	Deduction joining 3 equivalences to form equivalence of conjunctions. (Contributed by NM, 22-Apr-1994.)
|- ( ph -> ( ps <-> ch ) )   &    |- ( ph -> ( th <-> ta ) )   &    |- ( ph -> ( et <-> ze ) )   =>    |- ( ph -> ( ( ps /\ th /\ et ) <-> ( ch /\ ta /\ ze ) ) )
Theorem	3anbi12d 1325	Deduction conjoining and adding a conjunct to equivalences. (Contributed by NM, 8-Sep-2006.)
|- ( ph -> ( ps <-> ch ) )   &    |- ( ph -> ( th <-> ta ) )   =>    |- ( ph -> ( ( ps /\ th /\ et ) <-> ( ch /\ ta /\ et ) ) )
Theorem	3anbi13d 1326	Deduction conjoining and adding a conjunct to equivalences. (Contributed by NM, 8-Sep-2006.)
|- ( ph -> ( ps <-> ch ) )   &    |- ( ph -> ( th <-> ta ) )   =>    |- ( ph -> ( ( ps /\ et /\ th ) <-> ( ch /\ et /\ ta ) ) )
Theorem	3anbi23d 1327	Deduction conjoining and adding a conjunct to equivalences. (Contributed by NM, 8-Sep-2006.)
|- ( ph -> ( ps <-> ch ) )   &    |- ( ph -> ( th <-> ta ) )   =>    |- ( ph -> ( ( et /\ ps /\ th ) <-> ( et /\ ch /\ ta ) ) )
Theorem	3anbi1d 1328	Deduction adding conjuncts to an equivalence. (Contributed by NM, 8-Sep-2006.)
|- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( ( ps /\ th /\ ta ) <-> ( ch /\ th /\ ta ) ) )
Theorem	3anbi2d 1329	Deduction adding conjuncts to an equivalence. (Contributed by NM, 8-Sep-2006.)
|- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( ( th /\ ps /\ ta ) <-> ( th /\ ch /\ ta ) ) )
Theorem	3anbi3d 1330	Deduction adding conjuncts to an equivalence. (Contributed by NM, 8-Sep-2006.)
|- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( ( th /\ ta /\ ps ) <-> ( th /\ ta /\ ch ) ) )
Theorem	3anim123d 1331	Deduction joining 3 implications to form implication of conjunctions. (Contributed by NM, 24-Feb-2005.)
|- ( ph -> ( ps -> ch ) )   &    |- ( ph -> ( th -> ta ) )   &    |- ( ph -> ( et -> ze ) )   =>    |- ( ph -> ( ( ps /\ th /\ et ) -> ( ch /\ ta /\ ze ) ) )
Theorem	3orim123d 1332	Deduction joining 3 implications to form implication of disjunctions. (Contributed by NM, 4-Apr-1997.)
|- ( ph -> ( ps -> ch ) )   &    |- ( ph -> ( th -> ta ) )   &    |- ( ph -> ( et -> ze ) )   =>    |- ( ph -> ( ( ps \/ th \/ et ) -> ( ch \/ ta \/ ze ) ) )
Theorem	an6 1333	Rearrangement of 6 conjuncts. (Contributed by NM, 13-Mar-1995.)
|- ( ( ( ph /\ ps /\ ch ) /\ ( th /\ ta /\ et ) ) <-> ( ( ph /\ th ) /\ ( ps /\ ta ) /\ ( ch /\ et ) ) )
Theorem	3an6 1334	Analog of an4 586 for triple conjunction. (Contributed by Scott Fenton, 16-Mar-2011.) (Proof shortened by Andrew Salmon, 25-May-2011.)
|- ( ( ( ph /\ ps ) /\ ( ch /\ th ) /\ ( ta /\ et ) ) <-> ( ( ph /\ ch /\ ta ) /\ ( ps /\ th /\ et ) ) )
Theorem	3or6 1335	Analog of or4 772 for triple conjunction. (Contributed by Scott Fenton, 16-Mar-2011.)
|- ( ( ( ph \/ ps ) \/ ( ch \/ th ) \/ ( ta \/ et ) ) <-> ( ( ph \/ ch \/ ta ) \/ ( ps \/ th \/ et ) ) )
Theorem	mp3an1 1336	An inference based on modus ponens. (Contributed by NM, 21-Nov-1994.)
|- ph   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ( ps /\ ch ) -> th )
Theorem	mp3an2 1337	An inference based on modus ponens. (Contributed by NM, 21-Nov-1994.)
|- ps   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ( ph /\ ch ) -> th )
Theorem	mp3an3 1338	An inference based on modus ponens. (Contributed by NM, 21-Nov-1994.)
|- ch   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ( ph /\ ps ) -> th )
Theorem	mp3an12 1339	An inference based on modus ponens. (Contributed by NM, 13-Jul-2005.)
|- ph   &    |- ps   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ch -> th )
Theorem	mp3an13 1340	An inference based on modus ponens. (Contributed by NM, 14-Jul-2005.)
|- ph   &    |- ch   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ps -> th )
Theorem	mp3an23 1341	An inference based on modus ponens. (Contributed by NM, 14-Jul-2005.)
|- ps   &    |- ch   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ph -> th )
Theorem	mp3an1i 1342	An inference based on modus ponens. (Contributed by NM, 5-Jul-2005.)
|- ps   &    |- ( ph -> ( ( ps /\ ch /\ th ) -> ta ) )   =>    |- ( ph -> ( ( ch /\ th ) -> ta ) )
Theorem	mp3anl1 1343	An inference based on modus ponens. (Contributed by NM, 24-Feb-2005.)
|- ph   &    |- ( ( ( ph /\ ps /\ ch ) /\ th ) -> ta )   =>    |- ( ( ( ps /\ ch ) /\ th ) -> ta )
Theorem	mp3anl2 1344	An inference based on modus ponens. (Contributed by NM, 24-Feb-2005.)
|- ps   &    |- ( ( ( ph /\ ps /\ ch ) /\ th ) -> ta )   =>    |- ( ( ( ph /\ ch ) /\ th ) -> ta )
Theorem	mp3anl3 1345	An inference based on modus ponens. (Contributed by NM, 24-Feb-2005.)
|- ch   &    |- ( ( ( ph /\ ps /\ ch ) /\ th ) -> ta )   =>    |- ( ( ( ph /\ ps ) /\ th ) -> ta )
Theorem	mp3anr1 1346	An inference based on modus ponens. (Contributed by NM, 4-Nov-2006.)
|- ps   &    |- ( ( ph /\ ( ps /\ ch /\ th ) ) -> ta )   =>    |- ( ( ph /\ ( ch /\ th ) ) -> ta )
Theorem	mp3anr2 1347	An inference based on modus ponens. (Contributed by NM, 24-Nov-2006.)
|- ch   &    |- ( ( ph /\ ( ps /\ ch /\ th ) ) -> ta )   =>    |- ( ( ph /\ ( ps /\ th ) ) -> ta )
Theorem	mp3anr3 1348	An inference based on modus ponens. (Contributed by NM, 19-Oct-2007.)
|- th   &    |- ( ( ph /\ ( ps /\ ch /\ th ) ) -> ta )   =>    |- ( ( ph /\ ( ps /\ ch ) ) -> ta )
Theorem	mp3an 1349	An inference based on modus ponens. (Contributed by NM, 14-May-1999.)
|- ph   &    |- ps   &    |- ch   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- th
Theorem	mpd3an3 1350	An inference based on modus ponens. (Contributed by NM, 8-Nov-2007.)
|- ( ( ph /\ ps ) -> ch )   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ( ph /\ ps ) -> th )
Theorem	mpd3an23 1351	An inference based on modus ponens. (Contributed by NM, 4-Dec-2006.)
|- ( ph -> ps )   &    |- ( ph -> ch )   &    |- ( ( ph /\ ps /\ ch ) -> th )   =>    |- ( ph -> th )
Theorem	mp3and 1352	A deduction based on modus ponens. (Contributed by Mario Carneiro, 24-Dec-2016.)
|- ( ph -> ps )   &    |- ( ph -> ch )   &    |- ( ph -> th )   &    |- ( ph -> ( ( ps /\ ch /\ th ) -> ta ) )   =>    |- ( ph -> ta )
Theorem	mp3an12i 1353	mp3an 1349 with antecedents in standard conjunction form and with one hypothesis an implication. (Contributed by Alan Sare, 28-Aug-2016.)
|- ph   &    |- ps   &    |- ( ch -> th )   &    |- ( ( ph /\ ps /\ th ) -> ta )   =>    |- ( ch -> ta )
Theorem	mp3an2i 1354	mp3an 1349 with antecedents in standard conjunction form and with two hypotheses which are implications. (Contributed by Alan Sare, 28-Aug-2016.)
|- ph   &    |- ( ps -> ch )   &    |- ( ps -> th )   &    |- ( ( ph /\ ch /\ th ) -> ta )   =>    |- ( ps -> ta )
Theorem	mp3an3an 1355	mp3an 1349 with antecedents in standard conjunction form and with two hypotheses which are implications. (Contributed by Alan Sare, 28-Aug-2016.)
|- ph   &    |- ( ps -> ch )   &    |- ( th -> ta )   &    |- ( ( ph /\ ch /\ ta ) -> et )   =>    |- ( ( ps /\ th ) -> et )
Theorem	mp3an2ani 1356	An elimination deduction. (Contributed by Alan Sare, 17-Oct-2017.)
|- ph   &    |- ( ps -> ch )   &    |- ( ( ps /\ th ) -> ta )   &    |- ( ( ph /\ ch /\ ta ) -> et )   =>    |- ( ( ps /\ th ) -> et )
Theorem	biimp3a 1357	Infer implication from a logical equivalence. Similar to biimpa 296. (Contributed by NM, 4-Sep-2005.)
|- ( ( ph /\ ps ) -> ( ch <-> th ) )   =>    |- ( ( ph /\ ps /\ ch ) -> th )
Theorem	biimp3ar 1358	Infer implication from a logical equivalence. Similar to biimpar 297. (Contributed by NM, 2-Jan-2009.)
|- ( ( ph /\ ps ) -> ( ch <-> th ) )   =>    |- ( ( ph /\ ps /\ th ) -> ch )
Theorem	3anandis 1359	Inference that undistributes a triple conjunction in the antecedent. (Contributed by NM, 18-Apr-2007.)
|- ( ( ( ph /\ ps ) /\ ( ph /\ ch ) /\ ( ph /\ th ) ) -> ta )   =>    |- ( ( ph /\ ( ps /\ ch /\ th ) ) -> ta )
Theorem	3anandirs 1360	Inference that undistributes a triple conjunction in the antecedent. (Contributed by NM, 25-Jul-2006.) (Revised by NM, 18-Apr-2007.)
|- ( ( ( ph /\ th ) /\ ( ps /\ th ) /\ ( ch /\ th ) ) -> ta )   =>    |- ( ( ( ph /\ ps /\ ch ) /\ th ) -> ta )
Theorem	ecased 1361	Deduction form of disjunctive syllogism. (Contributed by Jim Kingdon, 9-Dec-2017.)
|- ( ph -> -. ch )   &    |- ( ph -> ( ps \/ ch ) )   =>    |- ( ph -> ps )
Theorem	ecase23d 1362	Variation of ecased 1361 with three disjuncts instead of two. (Contributed by NM, 22-Apr-1994.) (Revised by Jim Kingdon, 9-Dec-2017.)
|- ( ph -> -. ch )   &    |- ( ph -> -. th )   &    |- ( ph -> ( ps \/ ch \/ th ) )   =>    |- ( ph -> ps )
Theorem	3bior1fd 1363	A disjunction is equivalent to a threefold disjunction with single falsehood, analogous to biorf 745. (Contributed by Alexander van der Vekens, 8-Sep-2017.)
|- ( ph -> -. th )   =>    |- ( ph -> ( ( ch \/ ps ) <-> ( th \/ ch \/ ps ) ) )
Theorem	3bior1fand 1364	A disjunction is equivalent to a threefold disjunction with single falsehood of a conjunction. (Contributed by Alexander van der Vekens, 8-Sep-2017.)
|- ( ph -> -. th )   =>    |- ( ph -> ( ( ch \/ ps ) <-> ( ( th /\ ta ) \/ ch \/ ps ) ) )
Theorem	3bior2fd 1365	A wff is equivalent to its threefold disjunction with double falsehood, analogous to biorf 745. (Contributed by Alexander van der Vekens, 8-Sep-2017.)
|- ( ph -> -. th )   &    |- ( ph -> -. ch )   =>    |- ( ph -> ( ps <-> ( th \/ ch \/ ps ) ) )
Theorem	3biant1d 1366	A conjunction is equivalent to a threefold conjunction with single truth, analogous to biantrud 304. (Contributed by Alexander van der Vekens, 26-Sep-2017.)
|- ( ph -> th )   =>    |- ( ph -> ( ( ch /\ ps ) <-> ( th /\ ch /\ ps ) ) )
Theorem	intn3an1d 1367	Introduction of a triple conjunct inside a contradiction. (Contributed by FL, 27-Dec-2007.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)
|- ( ph -> -. ps )   =>    |- ( ph -> -. ( ps /\ ch /\ th ) )
Theorem	intn3an2d 1368	Introduction of a triple conjunct inside a contradiction. (Contributed by FL, 27-Dec-2007.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)
|- ( ph -> -. ps )   =>    |- ( ph -> -. ( ch /\ ps /\ th ) )
Theorem	intn3an3d 1369	Introduction of a triple conjunct inside a contradiction. (Contributed by FL, 27-Dec-2007.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)
|- ( ph -> -. ps )   =>    |- ( ph -> -. ( ch /\ th /\ ps ) )
1.2.12  True and false constants
1.2.12.1  Universal quantifier for use by df-tru Even though it is not ordinarily part of propositional calculus, the universal quantifier A. is introduced here so that the soundness of Definition df-tru 1375 can be checked by the same algorithm that is used for predicate calculus. Its first real use is in Axiom ax-5 1469 in the predicate calculus section below. For those who want propositional calculus to be self-contained, i.e., to use wff variables only, the alternate Definition dftru2 1380 may be adopted and this subsection moved down to the start of the subsection with wex 1514 below. However, the use of dftru2 1380 as a definition requires a more elaborate definition checking algorithm that we prefer to avoid.
Syntax	wal 1370	Extend wff definition to include the universal quantifier ("for all"). A. x ph is read " ph (phi) is true for all x". Typically, in its final application ph would be replaced with a wff containing a (free) occurrence of the variable x, for example x = y. In a universe with a finite number of objects, "for all" is equivalent to a big conjunction (AND) with one wff for each possible case of x. When the universe is infinite (as with set theory), such a propositional-calculus equivalent is not possible because an infinitely long formula has no meaning, but conceptually the idea is the same.
wff A. x ph
1.2.12.2  Equality predicate for use by df-tru Even though it is not ordinarily part of propositional calculus, the equality predicate = is introduced here so that the soundness of definition df-tru 1375 can be checked by the same algorithm as is used for predicate calculus. Its first real use is in Axiom ax-8 1526 in the predicate calculus section below. For those who want propositional calculus to be self-contained, i.e., to use wff variables only, the alternate definition dftru2 1380 may be adopted and this subsection moved down to just above weq 1525 below. However, the use of dftru2 1380 as a definition requires a more elaborate definition checking algorithm that we prefer to avoid.
Syntax	cv 1371	This syntax construction states that a variable x, which has been declared to be a setvar variable by $f statement vx, is also a class expression. This can be justified informally as follows. We know that the class builder { y | y e. x } is a class by cab 2190. Since (when y is distinct from x) we have x = { y | y e. x } by cvjust 2199, we can argue that the syntax " class x " can be viewed as an abbreviation for " class { y | y e. x }". See the discussion under the definition of class in [Jech] p. 4 showing that "Every set can be considered to be a class." While it is tempting and perhaps occasionally useful to view cv 1371 as a "type conversion" from a setvar variable to a class variable, keep in mind that cv 1371 is intrinsically no different from any other class-building syntax such as cab 2190, cun 3163, or c0 3459. For a general discussion of the theory of classes and the role of cv 1371, see https://us.metamath.org/mpeuni/mmset.html#class 1371. (The description above applies to set theory, not predicate calculus. The purpose of introducing class x here, and not in set theory where it belongs, is to allow us to express i.e. "prove" the weq 1525 of predicate calculus from the wceq 1372 of set theory, so that we don't overload the = connective with two syntax definitions. This is done to prevent ambiguity that would complicate some Metamath parsers.)
class x
Syntax	wceq 1372	Extend wff definition to include class equality. For a general discussion of the theory of classes, see https://us.metamath.org/mpeuni/mmset.html#class. (The purpose of introducing wff A = B here, and not in set theory where it belongs, is to allow us to express i.e. "prove" the weq 1525 of predicate calculus in terms of the wceq 1372 of set theory, so that we don't "overload" the = connective with two syntax definitions. This is done to prevent ambiguity that would complicate some Metamath parsers. For example, some parsers - although not the Metamath program - stumble on the fact that the = in x = y could be the = of either weq 1525 or wceq 1372, although mathematically it makes no difference. The class variables A and B are introduced temporarily for the purpose of this definition but otherwise not used in predicate calculus. See df-cleq 2197 for more information on the set theory usage of wceq 1372.)
wff A = B
1.2.12.3  Define the true and false constants
Syntax	wtru 1373	T. is a wff.
wff T.
Theorem	trujust 1374	Soundness justification theorem for df-tru 1375. (Contributed by Mario Carneiro, 17-Nov-2013.) (Revised by NM, 11-Jul-2019.)
|- ( ( A. x x = x -> A. x x = x ) <-> ( A. y y = y -> A. y y = y ) )
Definition	df-tru 1375	Definition of the truth value "true", or "verum", denoted by T.. This is a tautology, as proved by tru 1376. In this definition, an instance of id 19 is used as the definiens, although any tautology, such as an axiom, can be used in its place. This particular id 19 instance was chosen so this definition can be checked by the same algorithm that is used for predicate calculus. This definition should be referenced directly only by tru 1376, and other proofs should depend on tru 1376 (directly or indirectly) instead of this definition, since there are many alternate ways to define T.. (Contributed by Anthony Hart, 13-Oct-2010.) (Revised by NM, 11-Jul-2019.) (New usage is discouraged.)
|- ( T. <-> ( A. x x = x -> A. x x = x ) )
Theorem	tru 1376	The truth value T. is provable. (Contributed by Anthony Hart, 13-Oct-2010.)
|- T.
Syntax	wfal 1377	F. is a wff.
wff F.
Definition	df-fal 1378	Definition of the truth value "false", or "falsum", denoted by F.. See also df-tru 1375. (Contributed by Anthony Hart, 22-Oct-2010.)
|- ( F. <-> -. T. )
Theorem	fal 1379	The truth value F. is refutable. (Contributed by Anthony Hart, 22-Oct-2010.) (Proof shortened by Mel L. O'Cat, 11-Mar-2012.)
|- -. F.
Theorem	dftru2 1380	An alternate definition of "true". (Contributed by Anthony Hart, 13-Oct-2010.) (Revised by BJ, 12-Jul-2019.) (New usage is discouraged.)
|- ( T. <-> ( ph -> ph ) )
Theorem	mptru 1381	Eliminate T. as an antecedent. A proposition implied by T. is true. (Contributed by Mario Carneiro, 13-Mar-2014.)
|- ( T. -> ph )   =>    |- ph
Theorem	tbtru 1382	A proposition is equivalent to itself being equivalent to T.. (Contributed by Anthony Hart, 14-Aug-2011.)
|- ( ph <-> ( ph <-> T. ) )
Theorem	nbfal 1383	The negation of a proposition is equivalent to itself being equivalent to F.. (Contributed by Anthony Hart, 14-Aug-2011.)
|- ( -. ph <-> ( ph <-> F. ) )
Theorem	bitru 1384	A theorem is equivalent to truth. (Contributed by Mario Carneiro, 9-May-2015.)
|- ph   =>    |- ( ph <-> T. )
Theorem	bifal 1385	A contradiction is equivalent to falsehood. (Contributed by Mario Carneiro, 9-May-2015.)
|- -. ph   =>    |- ( ph <-> F. )
Theorem	falim 1386	The truth value F. implies anything. Also called the principle of explosion, or "ex falso quodlibet". (Contributed by FL, 20-Mar-2011.) (Proof shortened by Anthony Hart, 1-Aug-2011.)
|- ( F. -> ph )
Theorem	falimd 1387	The truth value F. implies anything. (Contributed by Mario Carneiro, 9-Feb-2017.)
|- ( ( ph /\ F. ) -> ps )
Theorem	trud 1388	Anything implies T.. (Contributed by FL, 20-Mar-2011.) (Proof shortened by Anthony Hart, 1-Aug-2011.)
|- ( ph -> T. )
Theorem	truan 1389	True can be removed from a conjunction. (Contributed by FL, 20-Mar-2011.) (Proof shortened by Wolf Lammen, 21-Jul-2019.)
|- ( ( T. /\ ph ) <-> ph )
Theorem	dfnot 1390	Given falsum, we can define the negation of a wff ph as the statement that a contradiction follows from assuming ph. (Contributed by Mario Carneiro, 9-Feb-2017.) (Proof shortened by Wolf Lammen, 21-Jul-2019.)
|- ( -. ph <-> ( ph -> F. ) )
Theorem	inegd 1391	Negation introduction rule from natural deduction. (Contributed by Mario Carneiro, 9-Feb-2017.)
|- ( ( ph /\ ps ) -> F. )   =>    |- ( ph -> -. ps )
Theorem	pm2.21fal 1392	If a wff and its negation are provable, then falsum is provable. (Contributed by Mario Carneiro, 9-Feb-2017.)
|- ( ph -> ps )   &    |- ( ph -> -. ps )   =>    |- ( ph -> F. )
Theorem	pclem6 1393	Negation inferred from embedded conjunct. (Contributed by NM, 20-Aug-1993.) (Proof rewritten by Jim Kingdon, 4-May-2018.)
|- ( ( ph <-> ( ps /\ -. ph ) ) -> -. ps )
1.2.13  Logical 'xor'
Syntax	wxo 1394	Extend wff definition to include exclusive disjunction ('xor').
wff ( ph \/_ ps )
Definition	df-xor 1395	Define exclusive disjunction (logical 'xor'). Return true if either the left or right, but not both, are true. Contrast with /\ (wa 104), \/ (wo 709), and -> (wi 4) . (Contributed by FL, 22-Nov-2010.) (Modified by Jim Kingdon, 1-Mar-2018.)
|- ( ( ph \/_ ps ) <-> ( ( ph \/ ps ) /\ -. ( ph /\ ps ) ) )
Theorem	xoranor 1396	One way of defining exclusive or. Equivalent to df-xor 1395. (Contributed by Jim Kingdon and Mario Carneiro, 1-Mar-2018.)
|- ( ( ph \/_ ps ) <-> ( ( ph \/ ps ) /\ ( -. ph \/ -. ps ) ) )
Theorem	excxor 1397	This tautology shows that xor is really exclusive. (Contributed by FL, 22-Nov-2010.) (Proof rewritten by Jim Kingdon, 5-May-2018.)
|- ( ( ph \/_ ps ) <-> ( ( ph /\ -. ps ) \/ ( -. ph /\ ps ) ) )
Theorem	xoror 1398	XOR implies OR. (Contributed by BJ, 19-Apr-2019.)
|- ( ( ph \/_ ps ) -> ( ph \/ ps ) )
Theorem	xorbi2d 1399	Deduction joining an equivalence and a left operand to form equivalence of exclusive-or. (Contributed by Jim Kingdon, 7-Oct-2018.)
|- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( ( th \/_ ps ) <-> ( th \/_ ch ) ) )
Theorem	xorbi1d 1400	Deduction joining an equivalence and a right operand to form equivalence of exclusive-or. (Contributed by Jim Kingdon, 7-Oct-2018.)
|- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( ( ps \/_ th ) <-> ( ch \/_ th ) ) )