P. 17 of Theorem List - Intuitionistic Logic Explorer

Theorem List for Intuitionistic Logic Explorer - 1601-1700   *Has distinct variable group(s)

Type	Label	Description
Statement
Theorem	hbbi 1601	If x is not free in ph and ps, it is not free in ( ph <-> ps ). (Contributed by NM, 5-Aug-1993.)
|- ( ph -> A. x ph )   &    |- ( ps -> A. x ps )   =>    |- ( ( ph <-> ps ) -> A. x ( ph <-> ps ) )
Theorem	hb3or 1602	If x is not free in ph, ps, and ch, it is not free in ( ph \/ ps \/ ch ). (Contributed by NM, 14-Sep-2003.)
|- ( ph -> A. x ph )   &    |- ( ps -> A. x ps )   &    |- ( ch -> A. x ch )   =>    |- ( ( ph \/ ps \/ ch ) -> A. x ( ph \/ ps \/ ch ) )
Theorem	hb3an 1603	If x is not free in ph, ps, and ch, it is not free in ( ph /\ ps /\ ch ). (Contributed by NM, 14-Sep-2003.)
|- ( ph -> A. x ph )   &    |- ( ps -> A. x ps )   &    |- ( ch -> A. x ch )   =>    |- ( ( ph /\ ps /\ ch ) -> A. x ( ph /\ ps /\ ch ) )
Theorem	hba2 1604	Lemma 24 of [Monk2] p. 114. (Contributed by NM, 29-May-2008.)
|- ( A. y A. x ph -> A. x A. y A. x ph )
Theorem	hbia1 1605	Lemma 23 of [Monk2] p. 114. (Contributed by NM, 29-May-2008.)
|- ( ( A. x ph -> A. x ps ) -> A. x ( A. x ph -> A. x ps ) )
Theorem	19.3h 1606	A wff may be quantified with a variable not free in it. Theorem 19.3 of [Margaris] p. 89. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 21-May-2007.)
|- ( ph -> A. x ph )   =>    |- ( A. x ph <-> ph )
Theorem	19.3 1607	A wff may be quantified with a variable not free in it. Theorem 19.3 of [Margaris] p. 89. (Contributed by NM, 5-Aug-1993.) (Revised by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   =>    |- ( A. x ph <-> ph )
Theorem	19.16 1608	Theorem 19.16 of [Margaris] p. 90. (Contributed by NM, 12-Mar-1993.)
|- F/ x ph   =>    |- ( A. x ( ph <-> ps ) -> ( ph <-> A. x ps ) )
Theorem	19.17 1609	Theorem 19.17 of [Margaris] p. 90. (Contributed by NM, 12-Mar-1993.)
|- F/ x ps   =>    |- ( A. x ( ph <-> ps ) -> ( A. x ph <-> ps ) )
Theorem	19.21h 1610	Theorem 19.21 of [Margaris] p. 90. The hypothesis can be thought of as " x is not free in ph". New proofs should use 19.21 1636 instead. (Contributed by NM, 5-Aug-1993.) (New usage is discouraged.)
|- ( ph -> A. x ph )   =>    |- ( A. x ( ph -> ps ) <-> ( ph -> A. x ps ) )
Theorem	19.21bi 1611	Inference from Theorem 19.21 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- ( ph -> A. x ps )   =>    |- ( ph -> ps )
Theorem	19.21bbi 1612	Inference removing double quantifier. (Contributed by NM, 20-Apr-1994.)
|- ( ph -> A. x A. y ps )   =>    |- ( ph -> ps )
Theorem	19.27h 1613	Theorem 19.27 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- ( ps -> A. x ps )   =>    |- ( A. x ( ph /\ ps ) <-> ( A. x ph /\ ps ) )
Theorem	19.27 1614	Theorem 19.27 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- F/ x ps   =>    |- ( A. x ( ph /\ ps ) <-> ( A. x ph /\ ps ) )
Theorem	19.28h 1615	Theorem 19.28 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- ( ph -> A. x ph )   =>    |- ( A. x ( ph /\ ps ) <-> ( ph /\ A. x ps ) )
Theorem	19.28 1616	Theorem 19.28 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- F/ x ph   =>    |- ( A. x ( ph /\ ps ) <-> ( ph /\ A. x ps ) )
Theorem	nfan1 1617	A closed form of nfan 1618. (Contributed by Mario Carneiro, 3-Oct-2016.)
|- F/ x ph   &    |- ( ph -> F/ x ps )   =>    |- F/ x ( ph /\ ps )
Theorem	nfan 1618	If x is not free in ph and ps, it is not free in ( ph /\ ps ). (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 13-Jan-2018.)
|- F/ x ph   &    |- F/ x ps   =>    |- F/ x ( ph /\ ps )
Theorem	nf3an 1619	If x is not free in ph, ps, and ch, it is not free in ( ph /\ ps /\ ch ). (Contributed by Mario Carneiro, 11-Aug-2016.)
|- F/ x ph   &    |- F/ x ps   &    |- F/ x ch   =>    |- F/ x ( ph /\ ps /\ ch )
Theorem	nford 1620	If in a context x is not free in ps and ch, it is not free in ( ps \/ ch ). (Contributed by Jim Kingdon, 29-Oct-2019.)
|- ( ph -> F/ x ps )   &    |- ( ph -> F/ x ch )   =>    |- ( ph -> F/ x ( ps \/ ch ) )
Theorem	nfand 1621	If in a context x is not free in ps and ch, it is not free in ( ps /\ ch ). (Contributed by Mario Carneiro, 7-Oct-2016.)
|- ( ph -> F/ x ps )   &    |- ( ph -> F/ x ch )   =>    |- ( ph -> F/ x ( ps /\ ch ) )
Theorem	nf3and 1622	Deduction form of bound-variable hypothesis builder nf3an 1619. (Contributed by NM, 17-Feb-2013.) (Revised by Mario Carneiro, 16-Oct-2016.)
|- ( ph -> F/ x ps )   &    |- ( ph -> F/ x ch )   &    |- ( ph -> F/ x th )   =>    |- ( ph -> F/ x ( ps /\ ch /\ th ) )
Theorem	hbim1 1623	A closed form of hbim 1598. (Contributed by NM, 5-Aug-1993.)
|- ( ph -> A. x ph )   &    |- ( ph -> ( ps -> A. x ps ) )   =>    |- ( ( ph -> ps ) -> A. x ( ph -> ps ) )
Theorem	nfim1 1624	A closed form of nfim 1625. (Contributed by NM, 5-Aug-1993.) (Revised by Mario Carneiro, 24-Sep-2016.) (Proof shortened by Wolf Lammen, 2-Jan-2018.)
|- F/ x ph   &    |- ( ph -> F/ x ps )   =>    |- F/ x ( ph -> ps )
Theorem	nfim 1625	If x is not free in ph and ps, it is not free in ( ph -> ps ). (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 2-Jan-2018.)
|- F/ x ph   &    |- F/ x ps   =>    |- F/ x ( ph -> ps )
Theorem	hbimd 1626	Deduction form of bound-variable hypothesis builder hbim 1598. (Contributed by NM, 1-Jan-2002.) (Revised by NM, 2-Feb-2015.)
|- ( ph -> A. x ph )   &    |- ( ph -> ( ps -> A. x ps ) )   &    |- ( ph -> ( ch -> A. x ch ) )   =>    |- ( ph -> ( ( ps -> ch ) -> A. x ( ps -> ch ) ) )
Theorem	nfor 1627	If x is not free in ph and ps, it is not free in ( ph \/ ps ). (Contributed by Jim Kingdon, 11-Mar-2018.)
|- F/ x ph   &    |- F/ x ps   =>    |- F/ x ( ph \/ ps )
Theorem	hbbid 1628	Deduction form of bound-variable hypothesis builder hbbi 1601. (Contributed by NM, 1-Jan-2002.)
|- ( ph -> A. x ph )   &    |- ( ph -> ( ps -> A. x ps ) )   &    |- ( ph -> ( ch -> A. x ch ) )   =>    |- ( ph -> ( ( ps <-> ch ) -> A. x ( ps <-> ch ) ) )
Theorem	nfal 1629	If x is not free in ph, it is not free in A. y ph. (Contributed by Mario Carneiro, 11-Aug-2016.) Remove dependency on ax-4 1563. (Revised by GG, 25-Aug-2024.)
|- F/ x ph   =>    |- F/ x A. y ph
Theorem	nfnf 1630	If x is not free in ph, it is not free in F/ y ph. (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 30-Dec-2017.)
|- F/ x ph   =>    |- F/ x F/ y ph
Theorem	nfalt 1631	Closed form of nfal 1629. (Contributed by Jim Kingdon, 11-May-2018.)
|- ( A. y F/ x ph -> F/ x A. y ph )
Theorem	nfa2 1632	Lemma 24 of [Monk2] p. 114. (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x A. y A. x ph
Theorem	nfia1 1633	Lemma 23 of [Monk2] p. 114. (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ( A. x ph -> A. x ps )
Theorem	19.21ht 1634	Closed form of Theorem 19.21 of [Margaris] p. 90. (Contributed by NM, 27-May-1997.) (New usage is discouraged.)
|- ( A. x ( ph -> A. x ph ) -> ( A. x ( ph -> ps ) <-> ( ph -> A. x ps ) ) )
Theorem	19.21t 1635	Closed form of Theorem 19.21 of [Margaris] p. 90. (Contributed by NM, 27-May-1997.)
|- ( F/ x ph -> ( A. x ( ph -> ps ) <-> ( ph -> A. x ps ) ) )
Theorem	19.21 1636	Theorem 19.21 of [Margaris] p. 90. The hypothesis can be thought of as " x is not free in ph". (Contributed by NM, 5-Aug-1993.) (Revised by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   =>    |- ( A. x ( ph -> ps ) <-> ( ph -> A. x ps ) )
Theorem	stdpc5 1637	An axiom scheme of standard predicate calculus that emulates Axiom 5 of [Mendelson] p. 69. The hypothesis F/ x ph can be thought of as emulating " x is not free in ph". With this definition, the meaning of "not free" is less restrictive than the usual textbook definition; for example x would not (for us) be free in x = x by nfequid 1754. This theorem scheme can be proved as a metatheorem of Mendelson's axiom system, even though it is slightly stronger than his Axiom 5. (Contributed by NM, 22-Sep-1993.) (Revised by Mario Carneiro, 12-Oct-2016.) (Proof shortened by Wolf Lammen, 1-Jan-2018.)
|- F/ x ph   =>    |- ( A. x ( ph -> ps ) -> ( ph -> A. x ps ) )
Theorem	nfimd 1638	If in a context x is not free in ps and ch, then it is not free in ( ps -> ch ). (Contributed by Mario Carneiro, 24-Sep-2016.) (Proof shortened by Wolf Lammen, 30-Dec-2017.)
|- ( ph -> F/ x ps )   &    |- ( ph -> F/ x ch )   =>    |- ( ph -> F/ x ( ps -> ch ) )
Theorem	aaanh 1639	Rearrange universal quantifiers. (Contributed by NM, 12-Aug-1993.)
|- ( ph -> A. y ph )   &    |- ( ps -> A. x ps )   =>    |- ( A. x A. y ( ph /\ ps ) <-> ( A. x ph /\ A. y ps ) )
Theorem	aaan 1640	Rearrange universal quantifiers. (Contributed by NM, 12-Aug-1993.)
|- F/ y ph   &    |- F/ x ps   =>    |- ( A. x A. y ( ph /\ ps ) <-> ( A. x ph /\ A. y ps ) )
Theorem	nfbid 1641	If in a context x is not free in ps and ch, then it is not free in ( ps <-> ch ). (Contributed by Mario Carneiro, 24-Sep-2016.) (Proof shortened by Wolf Lammen, 29-Dec-2017.)
|- ( ph -> F/ x ps )   &    |- ( ph -> F/ x ch )   =>    |- ( ph -> F/ x ( ps <-> ch ) )
Theorem	nfbi 1642	If x is not free in ph and ps, then it is not free in ( ph <-> ps ). (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 2-Jan-2018.)
|- F/ x ph   &    |- F/ x ps   =>    |- F/ x ( ph <-> ps )
1.3.7  The existential quantifier
Theorem	19.8a 1643	If a wff is true, then it is true for at least one instance. Special case of Theorem 19.8 of [Margaris] p. 89. (Contributed by NM, 5-Aug-1993.)
|- ( ph -> E. x ph )
Theorem	19.8ad 1644	If a wff is true, it is true for at least one instance. Deduction form of 19.8a 1643. (Contributed by DAW, 13-Feb-2017.)
|- ( ph -> ps )   =>    |- ( ph -> E. x ps )
Theorem	19.23bi 1645	Inference from Theorem 19.23 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- ( E. x ph -> ps )   =>    |- ( ph -> ps )
Theorem	exlimih 1646	Inference from Theorem 19.23 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 13-May-2011.)
|- ( ps -> A. x ps )   &    |- ( ph -> ps )   =>    |- ( E. x ph -> ps )
Theorem	exlimi 1647	Inference from Theorem 19.23 of [Margaris] p. 90. (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ps   &    |- ( ph -> ps )   =>    |- ( E. x ph -> ps )
Theorem	exlimd2 1648	Deduction from Theorem 19.23 of [Margaris] p. 90. Similar to exlimdh 1649 but with one slightly different hypothesis. (Contributed by Jim Kingdon, 30-Dec-2017.)
|- ( ph -> A. x ph )   &    |- ( ph -> ( ch -> A. x ch ) )   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( E. x ps -> ch ) )
Theorem	exlimdh 1649	Deduction from Theorem 19.23 of [Margaris] p. 90. (Contributed by NM, 28-Jan-1997.)
|- ( ph -> A. x ph )   &    |- ( ch -> A. x ch )   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( E. x ps -> ch ) )
Theorem	exlimd 1650	Deduction from Theorem 19.9 of [Margaris] p. 89. (Contributed by Mario Carneiro, 24-Sep-2016.) (Proof rewritten by Jim Kingdon, 18-Jun-2018.)
|- F/ x ph   &    |- F/ x ch   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( E. x ps -> ch ) )
Theorem	exlimiv 1651*	Inference from Theorem 19.23 of [Margaris] p. 90. This inference, along with our many variants is used to implement a metatheorem called "Rule C" that is given in many logic textbooks. See, for example, Rule C in [Mendelson] p. 81, Rule C in [Margaris] p. 40, or Rule C in Hirst and Hirst's A Primer for Logic and Proof p. 59 (PDF p. 65) at http://www.mathsci.appstate.edu/~jlh/primer/hirst.pdf. In informal proofs, the statement "Let C be an element such that..." almost always means an implicit application of Rule C. In essence, Rule C states that if we can prove that some element x exists satisfying a wff, i.e. E. x ph ( x ) where ph ( x ) has x free, then we can use ph ( C ) as a hypothesis for the proof where C is a new (ficticious) constant not appearing previously in the proof, nor in any axioms used, nor in the theorem to be proved. The purpose of Rule C is to get rid of the existential quantifier. We cannot do this in Metamath directly. Instead, we use the original ph (containing x) as an antecedent for the main part of the proof. We eventually arrive at ( ph -> ps ) where ps is the theorem to be proved and does not contain x. Then we apply exlimiv 1651 to arrive at ( E. x ph -> ps ). Finally, we separately prove E. x ph and detach it with modus ponens ax-mp 5 to arrive at the final theorem ps. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 25-Jul-2012.)
|- ( ph -> ps )   =>    |- ( E. x ph -> ps )
Theorem	exim 1652	Theorem 19.22 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 4-Jul-2014.)
|- ( A. x ( ph -> ps ) -> ( E. x ph -> E. x ps ) )
Theorem	eximi 1653	Inference adding existential quantifier to antecedent and consequent. (Contributed by NM, 5-Aug-1993.)
|- ( ph -> ps )   =>    |- ( E. x ph -> E. x ps )
Theorem	2eximi 1654	Inference adding 2 existential quantifiers to antecedent and consequent. (Contributed by NM, 3-Feb-2005.)
|- ( ph -> ps )   =>    |- ( E. x E. y ph -> E. x E. y ps )
Theorem	eximii 1655	Inference associated with eximi 1653. (Contributed by BJ, 3-Feb-2018.)
|- E. x ph   &    |- ( ph -> ps )   =>    |- E. x ps
Theorem	alinexa 1656	A transformation of quantifiers and logical connectives. (Contributed by NM, 19-Aug-1993.)
|- ( A. x ( ph -> -. ps ) <-> -. E. x ( ph /\ ps ) )
Theorem	exbi 1657	Theorem 19.18 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- ( A. x ( ph <-> ps ) -> ( E. x ph <-> E. x ps ) )
Theorem	exbii 1658	Inference adding existential quantifier to both sides of an equivalence. (Contributed by NM, 24-May-1994.)
|- ( ph <-> ps )   =>    |- ( E. x ph <-> E. x ps )
Theorem	2exbii 1659	Inference adding 2 existential quantifiers to both sides of an equivalence. (Contributed by NM, 16-Mar-1995.)
|- ( ph <-> ps )   =>    |- ( E. x E. y ph <-> E. x E. y ps )
Theorem	3exbii 1660	Inference adding 3 existential quantifiers to both sides of an equivalence. (Contributed by NM, 2-May-1995.)
|- ( ph <-> ps )   =>    |- ( E. x E. y E. z ph <-> E. x E. y E. z ps )
Theorem	exancom 1661	Commutation of conjunction inside an existential quantifier. (Contributed by NM, 18-Aug-1993.)
|- ( E. x ( ph /\ ps ) <-> E. x ( ps /\ ph ) )
Theorem	alrimdd 1662	Deduction from Theorem 19.21 of [Margaris] p. 90. (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   &    |- ( ph -> F/ x ps )   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( ps -> A. x ch ) )
Theorem	alrimd 1663	Deduction from Theorem 19.21 of [Margaris] p. 90. (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   &    |- F/ x ps   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( ps -> A. x ch ) )
Theorem	eximdh 1664	Deduction from Theorem 19.22 of [Margaris] p. 90. (Contributed by NM, 20-May-1996.)
|- ( ph -> A. x ph )   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( E. x ps -> E. x ch ) )
Theorem	eximd 1665	Deduction from Theorem 19.22 of [Margaris] p. 90. (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   &    |- ( ph -> ( ps -> ch ) )   =>    |- ( ph -> ( E. x ps -> E. x ch ) )
Theorem	nexd 1666	Deduction for generalization rule for negated wff. (Contributed by NM, 2-Jan-2002.)
|- ( ph -> A. x ph )   &    |- ( ph -> -. ps )   =>    |- ( ph -> -. E. x ps )
Theorem	exbidh 1667	Formula-building rule for existential quantifier (deduction form). (Contributed by NM, 5-Aug-1993.)
|- ( ph -> A. x ph )   &    |- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( E. x ps <-> E. x ch ) )
Theorem	albid 1668	Formula-building rule for universal quantifier (deduction form). (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   &    |- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( A. x ps <-> A. x ch ) )
Theorem	exbid 1669	Formula-building rule for existential quantifier (deduction form). (Contributed by Mario Carneiro, 24-Sep-2016.)
|- F/ x ph   &    |- ( ph -> ( ps <-> ch ) )   =>    |- ( ph -> ( E. x ps <-> E. x ch ) )
Theorem	exsimpl 1670	Simplification of an existentially quantified conjunction. (Contributed by Rodolfo Medina, 25-Sep-2010.) (Proof shortened by Andrew Salmon, 29-Jun-2011.)
|- ( E. x ( ph /\ ps ) -> E. x ph )
Theorem	exsimpr 1671	Simplification of an existentially quantified conjunction. (Contributed by Rodolfo Medina, 25-Sep-2010.) (Proof shortened by Andrew Salmon, 29-Jun-2011.)
|- ( E. x ( ph /\ ps ) -> E. x ps )
Theorem	alexdc 1672	Theorem 19.6 of [Margaris] p. 89, given a decidability condition. The forward direction holds for all propositions, as seen at alexim 1698. (Contributed by Jim Kingdon, 2-Jun-2018.)
|- ( A. xDECID ph -> ( A. x ph <-> -. E. x -. ph ) )
Theorem	19.29 1673	Theorem 19.29 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Andrew Salmon, 13-May-2011.)
|- ( ( A. x ph /\ E. x ps ) -> E. x ( ph /\ ps ) )
Theorem	19.29r 1674	Variation of Theorem 19.29 of [Margaris] p. 90. (Contributed by NM, 18-Aug-1993.)
|- ( ( E. x ph /\ A. x ps ) -> E. x ( ph /\ ps ) )
Theorem	19.29r2 1675	Variation of Theorem 19.29 of [Margaris] p. 90 with double quantification. (Contributed by NM, 3-Feb-2005.)
|- ( ( E. x E. y ph /\ A. x A. y ps ) -> E. x E. y ( ph /\ ps ) )
Theorem	19.29x 1676	Variation of Theorem 19.29 of [Margaris] p. 90 with mixed quantification. (Contributed by NM, 11-Feb-2005.)
|- ( ( E. x A. y ph /\ A. x E. y ps ) -> E. x E. y ( ph /\ ps ) )
Theorem	19.35-1 1677	Forward direction of Theorem 19.35 of [Margaris] p. 90. The converse holds for classical logic but not (for all propositions) in intuitionistic logic. (Contributed by Mario Carneiro, 2-Feb-2015.)
|- ( E. x ( ph -> ps ) -> ( A. x ph -> E. x ps ) )
Theorem	19.35i 1678	Inference from Theorem 19.35 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 2-Feb-2015.)
|- E. x ( ph -> ps )   =>    |- ( A. x ph -> E. x ps )
Theorem	19.25 1679	Theorem 19.25 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 2-Feb-2015.)
|- ( A. y E. x ( ph -> ps ) -> ( E. y A. x ph -> E. y E. x ps ) )
Theorem	19.30dc 1680	Theorem 19.30 of [Margaris] p. 90, with an additional decidability condition. (Contributed by Jim Kingdon, 21-Jul-2018.)
|- (DECID E. x ps -> ( A. x ( ph \/ ps ) -> ( A. x ph \/ E. x ps ) ) )
Theorem	19.43 1681	Theorem 19.43 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Mario Carneiro, 2-Feb-2015.)
|- ( E. x ( ph \/ ps ) <-> ( E. x ph \/ E. x ps ) )
Theorem	19.33b2 1682	The antecedent provides a condition implying the converse of 19.33 1537. Compare Theorem 19.33 of [Margaris] p. 90. This variation of 19.33bdc 1683 is intuitionistically valid without a decidability condition. (Contributed by Mario Carneiro, 2-Feb-2015.)
|- ( ( -. E. x ph \/ -. E. x ps ) -> ( A. x ( ph \/ ps ) <-> ( A. x ph \/ A. x ps ) ) )
Theorem	19.33bdc 1683	Converse of 19.33 1537 given -. ( E. x ph /\ E. x ps ) and a decidability condition. Compare Theorem 19.33 of [Margaris] p. 90. For a version which does not require a decidability condition, see 19.33b2 1682 (Contributed by Jim Kingdon, 23-Apr-2018.)
|- (DECID E. x ph -> ( -. ( E. x ph /\ E. x ps ) -> ( A. x ( ph \/ ps ) <-> ( A. x ph \/ A. x ps ) ) ) )
Theorem	19.40 1684	Theorem 19.40 of [Margaris] p. 90. (Contributed by NM, 5-Aug-1993.)
|- ( E. x ( ph /\ ps ) -> ( E. x ph /\ E. x ps ) )
Theorem	19.40-2 1685	Theorem *11.42 in [WhiteheadRussell] p. 163. Theorem 19.40 of [Margaris] p. 90 with 2 quantifiers. (Contributed by Andrew Salmon, 24-May-2011.)
|- ( E. x E. y ( ph /\ ps ) -> ( E. x E. y ph /\ E. x E. y ps ) )
Theorem	exintrbi 1686	Add/remove a conjunct in the scope of an existential quantifier. (Contributed by Raph Levien, 3-Jul-2006.)
|- ( A. x ( ph -> ps ) -> ( E. x ph <-> E. x ( ph /\ ps ) ) )
Theorem	exintr 1687	Introduce a conjunct in the scope of an existential quantifier. (Contributed by NM, 11-Aug-1993.)
|- ( A. x ( ph -> ps ) -> ( E. x ph -> E. x ( ph /\ ps ) ) )
Theorem	alsyl 1688	Theorem *10.3 in [WhiteheadRussell] p. 150. (Contributed by Andrew Salmon, 8-Jun-2011.)
|- ( ( A. x ( ph -> ps ) /\ A. x ( ps -> ch ) ) -> A. x ( ph -> ch ) )
Theorem	hbex 1689	If x is not free in ph, it is not free in E. y ph. (Contributed by NM, 5-Aug-1993.) (Revised by NM, 2-Feb-2015.)
|- ( ph -> A. x ph )   =>    |- ( E. y ph -> A. x E. y ph )
Theorem	nfex 1690	If x is not free in ph, it is not free in E. y ph. (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 30-Dec-2017.)
|- F/ x ph   =>    |- F/ x E. y ph
Theorem	19.2 1691	Theorem 19.2 of [Margaris] p. 89, generalized to use two setvar variables. (Contributed by O'Cat, 31-Mar-2008.)
|- ( A. x ph -> E. y ph )
Theorem	i19.24 1692	Theorem 19.24 of [Margaris] p. 90, with an additional hypothesis. The hypothesis is the converse of 19.35-1 1677, and is a theorem of classical logic, but in intuitionistic logic it will only be provable for some propositions. (Contributed by Jim Kingdon, 22-Jul-2018.)
|- ( ( A. x ph -> E. x ps ) -> E. x ( ph -> ps ) )   =>    |- ( ( A. x ph -> A. x ps ) -> E. x ( ph -> ps ) )
Theorem	i19.39 1693	Theorem 19.39 of [Margaris] p. 90, with an additional hypothesis. The hypothesis is the converse of 19.35-1 1677, and is a theorem of classical logic, but in intuitionistic logic it will only be provable for some propositions. (Contributed by Jim Kingdon, 22-Jul-2018.)
|- ( ( A. x ph -> E. x ps ) -> E. x ( ph -> ps ) )   =>    |- ( ( E. x ph -> E. x ps ) -> E. x ( ph -> ps ) )
Theorem	19.9ht 1694	A closed version of one direction of 19.9 1697. (Contributed by NM, 5-Aug-1993.)
|- ( A. x ( ph -> A. x ph ) -> ( E. x ph -> ph ) )
Theorem	19.9t 1695	A closed version of 19.9 1697. (Contributed by NM, 5-Aug-1993.) (Revised by Mario Carneiro, 24-Sep-2016.) (Proof shortended by Wolf Lammen, 30-Dec-2017.)
|- ( F/ x ph -> ( E. x ph <-> ph ) )
Theorem	19.9h 1696	A wff may be existentially quantified with a variable not free in it. Theorem 19.9 of [Margaris] p. 89. (Contributed by FL, 24-Mar-2007.)
|- ( ph -> A. x ph )   =>    |- ( E. x ph <-> ph )
Theorem	19.9 1697	A wff may be existentially quantified with a variable not free in it. Theorem 19.9 of [Margaris] p. 89. (Contributed by FL, 24-Mar-2007.) (Revised by Mario Carneiro, 24-Sep-2016.) (Proof shortened by Wolf Lammen, 30-Dec-2017.)
|- F/ x ph   =>    |- ( E. x ph <-> ph )
Theorem	alexim 1698	One direction of Theorem 19.6 of [Margaris] p. 89. The converse holds given a decidability condition, as seen at alexdc 1672. (Contributed by Jim Kingdon, 2-Jul-2018.)
|- ( A. x ph -> -. E. x -. ph )
Theorem	exnalim 1699	One direction of Theorem 19.14 of [Margaris] p. 90. The converse holds in classical but not in intuitionistic logic. (Contributed by Jim Kingdon, 15-Jul-2018.)
|- ( E. x -. ph -> -. A. x ph )
Theorem	exanaliim 1700	A transformation of quantifiers and logical connectives. The converse holds in classical but not in intuitionistic logic. (Contributed by Jim Kingdon, 15-Jul-2018.)
|- ( E. x ( ph /\ -. ps ) -> -. A. x ( ph -> ps ) )