Theorem csbco 3145

Description: Composition law for chained substitutions into a class. (Contributed by NM, 10-Nov-2005.)

Assertion

Ref	Expression
csbco	|- [_A / y]_[_y / x]_B = [_A / x]_B

Distinct variable group:   y,B

Allowed substitution hints:   A(x,y)   B(x)

Proof of Theorem csbco

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-csb 3137	. . . . . 6 |- [_y / x]_B = {z | [.y / x ].z e. B}
2	1	abeq2i 2460	. . . . 5 |- (z e. [_y / x]_B <-> [.y / x ].z e. B)
3	2	sbcbii 3101	. . . 4 |- ( [.A / y ].z e. [_y / x]_B <-> [.A / y ]. [.y / x ].z e. B)
4		sbcco 3068	. . . 4 |- ( [.A / y ]. [.y / x ].z e. B <-> [.A / x ].z e. B)
5	3, 4	bitri 240	. . 3 |- ( [.A / y ].z e. [_y / x]_B <-> [.A / x ].z e. B)
6	5	abbii 2465	. 2 |- {z | [.A / y ].z e. [_y / x]_B} = {z | [.A / x ].z e. B}
7		df-csb 3137	. 2 |- [_A / y]_[_y / x]_B = {z | [.A / y ].z e. [_y / x]_B}
8		df-csb 3137	. 2 |- [_A / x]_B = {z | [.A / x ].z e. B}
9	6, 7, 8	3eqtr4i 2383	1 |- [_A / y]_[_y / x]_B = [_A / x]_B

Syntax hints:   = wceq 1642   e. wcel 1710  {cab 2339   [.wsbc 3046  [_csb 3136

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2478  df-v 2861  df-sbc 3047  df-csb 3137

This theorem is referenced by:  csbvarg  3163  csbnest1g  3188  eqerlem  5960