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Theorem csbiotag 4838
 Description: Class substitution within a description binder. (Contributed by Scott Fenton, 6-Oct-2017.)
Assertion
Ref Expression
csbiotag (A 𝑉A / x(℩yφ) = (℩y[A / x]φ))
Distinct variable groups:   y,A   x,y
Allowed substitution hints:   φ(x,y)   A(x)   𝑉(x,y)

Proof of Theorem csbiotag
Dummy variable z is distinct from all other variables.
StepHypRef Expression
1 csbeq1 2849 . . 3 (z = Az / x(℩yφ) = A / x(℩yφ))
2 dfsbcq2 2761 . . . 4 (z = A → ([z / x]φ[A / x]φ))
32iotabidv 4831 . . 3 (z = A → (℩y[z / x]φ) = (℩y[A / x]φ))
41, 3eqeq12d 2051 . 2 (z = A → (z / x(℩yφ) = (℩y[z / x]φ) ↔ A / x(℩yφ) = (℩y[A / x]φ)))
5 vex 2554 . . 3 z V
6 nfs1v 1812 . . . 4 x[z / x]φ
76nfiotaxy 4814 . . 3 x(℩y[z / x]φ)
8 sbequ12 1651 . . . 4 (x = z → (φ ↔ [z / x]φ))
98iotabidv 4831 . . 3 (x = z → (℩yφ) = (℩y[z / x]φ))
105, 7, 9csbief 2885 . 2 z / x(℩yφ) = (℩y[z / x]φ)
114, 10vtoclg 2607 1 (A 𝑉A / x(℩yφ) = (℩y[A / x]φ))
 Colors of variables: wff set class Syntax hints:   → wi 4   = wceq 1242   ∈ wcel 1390  [wsb 1642  [wsbc 2758  ⦋csb 2846  ℩cio 4808 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 629  ax-5 1333  ax-7 1334  ax-gen 1335  ax-ie1 1379  ax-ie2 1380  ax-8 1392  ax-10 1393  ax-11 1394  ax-i12 1395  ax-bnd 1396  ax-4 1397  ax-17 1416  ax-i9 1420  ax-ial 1424  ax-i5r 1425  ax-ext 2019 This theorem depends on definitions:  df-bi 110  df-3an 886  df-tru 1245  df-nf 1347  df-sb 1643  df-clab 2024  df-cleq 2030  df-clel 2033  df-nfc 2164  df-rex 2306  df-v 2553  df-sbc 2759  df-csb 2847  df-sn 3373  df-uni 3572  df-iota 4810 This theorem is referenced by:  csbfv12g  5152
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