Theorem csbidmg 3101

Description: Idempotent law for class substitutions. (Contributed by NM, 1-Mar-2008.)

Assertion

Ref	Expression
csbidmg	|- ( A e. V -> [_ A / x ]_ [_ A / x ]_ B = [_ A / x ]_ B )

Distinct variable group:   x, A

Allowed substitution hints:   B( x)   V( x)

Proof of Theorem csbidmg

Step	Hyp	Ref	Expression
1		elex 2737	. 2 |- ( A e. V -> A e. _V )
2		csbnest1g 3100	. . 3 |- ( A e. _V -> [_ A / x ]_ [_ A / x ]_ B = [_ [_ A / x ]_ A / x ]_ B )
3		csbconstg 3059	. . . 4 |- ( A e. _V -> [_ A / x ]_ A = A )
4	3	csbeq1d 3052	. . 3 |- ( A e. _V -> [_ [_ A / x ]_ A / x ]_ B = [_ A / x ]_ B )
5	2, 4	eqtrd 2198	. 2 |- ( A e. _V -> [_ A / x ]_ [_ A / x ]_ B = [_ A / x ]_ B )
6	1, 5	syl 14	1 |- ( A e. V -> [_ A / x ]_ [_ A / x ]_ B = [_ A / x ]_ B )

Syntax hints:   -> wi 4   = wceq 1343   e. wcel 2136   _Vcvv 2726   [_csb 3045

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 699  ax-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523  ax-ext 2147

This theorem depends on definitions:  df-bi 116  df-3an 970  df-tru 1346  df-nf 1449  df-sb 1751  df-clab 2152  df-cleq 2158  df-clel 2161  df-nfc 2297  df-v 2728  df-sbc 2952  df-csb 3046

This theorem is referenced by: (None)