Theorem sbc2or 3444

Description: The disjunction of two equivalences for class substitution does not require a class existence hypothesis. This theorem tells us that there are only 2 possibilities for [ A / x ] ph behavior at proper classes, matching the sbc5 3460 (false) and sbc6 3462 (true) conclusions. This is interesting since dfsbcq 3437 and dfsbcq2 3438 (from which it is derived) do not appear to say anything obvious about proper class behavior. Note that this theorem does not tell us that it is always one or the other at proper classes; it could "flip" between false (the first disjunct) and true (the second disjunct) as a function of some other variable y that ph or A may contain. (Contributed by NM, 11-Oct-2004.) (Proof modification is discouraged.)

Assertion

Ref	Expression
sbc2or	|- ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> A. x ( x = A -> ph ) ) )

Distinct variable group:   x, A

Allowed substitution hint:   ph( x)

Proof of Theorem sbc2or

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		dfsbcq2 3438	. . . 4 |- ( y = A -> ( [ y / x ] ph <-> [. A / x ]. ph ) )
2		eqeq2 2633	. . . . . 6 |- ( y = A -> ( x = y <-> x = A ) )
3	2	anbi1d 741	. . . . 5 |- ( y = A -> ( ( x = y /\ ph ) <-> ( x = A /\ ph ) ) )
4	3	exbidv 1850	. . . 4 |- ( y = A -> ( E. x ( x = y /\ ph ) <-> E. x ( x = A /\ ph ) ) )
5		sb5 2430	. . . 4 |- ( [ y / x ] ph <-> E. x ( x = y /\ ph ) )
6	1, 4, 5	vtoclbg 3267	. . 3 |- ( A e. _V -> ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) )
7	6	orcd 407	. 2 |- ( A e. _V -> ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> A. x ( x = A -> ph ) ) ) )
8		pm5.15 933	. . 3 |- ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> -. E. x ( x = A /\ ph ) ) )
9		vex 3203	. . . . . . . . . 10 |- x e. _V
10		eleq1 2689	. . . . . . . . . 10 |- ( x = A -> ( x e. _V <-> A e. _V ) )
11	9, 10	mpbii 223	. . . . . . . . 9 |- ( x = A -> A e. _V )
12	11	adantr 481	. . . . . . . 8 |- ( ( x = A /\ ph ) -> A e. _V )
13	12	con3i 150	. . . . . . 7 |- ( -. A e. _V -> -. ( x = A /\ ph ) )
14	13	nexdv 1864	. . . . . 6 |- ( -. A e. _V -> -. E. x ( x = A /\ ph ) )
15	11	con3i 150	. . . . . . . 8 |- ( -. A e. _V -> -. x = A )
16	15	pm2.21d 118	. . . . . . 7 |- ( -. A e. _V -> ( x = A -> ph ) )
17	16	alrimiv 1855	. . . . . 6 |- ( -. A e. _V -> A. x ( x = A -> ph ) )
18	14, 17	2thd 255	. . . . 5 |- ( -. A e. _V -> ( -. E. x ( x = A /\ ph ) <-> A. x ( x = A -> ph ) ) )
19	18	bibi2d 332	. . . 4 |- ( -. A e. _V -> ( ( [. A / x ]. ph <-> -. E. x ( x = A /\ ph ) ) <-> ( [. A / x ]. ph <-> A. x ( x = A -> ph ) ) ) )
20	19	orbi2d 738	. . 3 |- ( -. A e. _V -> ( ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> -. E. x ( x = A /\ ph ) ) ) <-> ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> A. x ( x = A -> ph ) ) ) ) )
21	8, 20	mpbii 223	. 2 |- ( -. A e. _V -> ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> A. x ( x = A -> ph ) ) ) )
22	7, 21	pm2.61i 176	1 |- ( ( [. A / x ]. ph <-> E. x ( x = A /\ ph ) ) \/ ( [. A / x ]. ph <-> A. x ( x = A -> ph ) ) )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 196   \/ wo 383   /\ wa 384   A.wal 1481   = wceq 1483   E.wex 1704   [wsb 1880   e. wcel 1990   _Vcvv 3200   [.wsbc 3435

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1722  ax-4 1737  ax-5 1839  ax-6 1888  ax-7 1935  ax-9 1999  ax-10 2019  ax-12 2047  ax-13 2246  ax-ext 2602

This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1486  df-ex 1705  df-nf 1710  df-sb 1881  df-clab 2609  df-cleq 2615  df-clel 2618  df-v 3202  df-sbc 3436

This theorem is referenced by: (None)