Theorem dedth4vOLD 3014

Description: Weak deduction theorem for eliminating a hypothesis with 4 class variables. See comments in dedth2v 3018.

Hypotheses

Ref	Expression
dedth4vOLD.1	|- (A = if(ph, A, R) -> (ps <-> ch))
dedth4vOLD.2	|- (B = if(ph, B, S) -> (ch <-> th))
dedth4vOLD.3	|- (C = if(ph, C, T) -> (th <-> ta))
dedth4vOLD.4	|- (D = if(ph, D, U) -> (ta <-> et))
dedth4vOLD.5	|- et

Assertion

Ref	Expression
dedth4vOLD	|- (ph -> ps)

Proof of Theorem dedth4vOLD

Step	Hyp	Ref	Expression
1		dedth4vOLD.5	. 2 |- et
2		iftrue 2989	. . . . . 6 |- (ph -> if(ph, A, R) = A)
3	2	eqcomd 1889	. . . . 5 |- (ph -> A = if(ph, A, R))
4		dedth4vOLD.1	. . . . 5 |- (A = if(ph, A, R) -> (ps <-> ch))
5	3, 4	syl 12	. . . 4 |- (ph -> (ps <-> ch))
6		iftrue 2989	. . . . . 6 |- (ph -> if(ph, B, S) = B)
7	6	eqcomd 1889	. . . . 5 |- (ph -> B = if(ph, B, S))
8		dedth4vOLD.2	. . . . 5 |- (B = if(ph, B, S) -> (ch <-> th))
9	7, 8	syl 12	. . . 4 |- (ph -> (ch <-> th))
10	5, 9	bitrd 587	. . 3 |- (ph -> (ps <-> th))
11		iftrue 2989	. . . . 5 |- (ph -> if(ph, C, T) = C)
12	11	eqcomd 1889	. . . 4 |- (ph -> C = if(ph, C, T))
13		dedth4vOLD.3	. . . 4 |- (C = if(ph, C, T) -> (th <-> ta))
14	12, 13	syl 12	. . 3 |- (ph -> (th <-> ta))
15		iftrue 2989	. . . . 5 |- (ph -> if(ph, D, U) = D)
16	15	eqcomd 1889	. . . 4 |- (ph -> D = if(ph, D, U))
17		dedth4vOLD.4	. . . 4 |- (D = if(ph, D, U) -> (ta <-> et))
18	16, 17	syl 12	. . 3 |- (ph -> (ta <-> et))
19	10, 14, 18	3bitrd 603	. 2 |- (ph -> (ps <-> et))
20	1, 19	mpbiri 211	1 |- (ph -> ps)

Syntax hints:   -> wi 3   <-> wb 163   = wceq 1298  ifcif 2982

This theorem is referenced by:  dedth4v 3020

This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7  ax-7 1304  ax-gen 1305  ax-8 1306  ax-10 1308  ax-12 1310  ax-17 1317  ax-4 1319  ax-5o 1321  ax-6o 1324  ax-9o 1481  ax-10o 1500  ax-16 1580  ax-11o 1588  ax-ext 1865

This theorem depends on definitions:  df-bi 164  df-or 241  df-an 242  df-ex 1327  df-sb 1536  df-clab 1872  df-cleq 1877  df-clel 1880  df-if 2983

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