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Theorem ssint 4465
 Description: Subclass of a class intersection. Theorem 5.11(viii) of [Monk1] p. 52 and its converse. (Contributed by NM, 14-Oct-1999.)
Assertion
Ref Expression
ssint (𝐴 𝐵 ↔ ∀𝑥𝐵 𝐴𝑥)
Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Proof of Theorem ssint
Dummy variable 𝑦 is distinct from all other variables.
StepHypRef Expression
1 dfss3 3578 . 2 (𝐴 𝐵 ↔ ∀𝑦𝐴 𝑦 𝐵)
2 vex 3193 . . . 4 𝑦 ∈ V
32elint2 4454 . . 3 (𝑦 𝐵 ↔ ∀𝑥𝐵 𝑦𝑥)
43ralbii 2976 . 2 (∀𝑦𝐴 𝑦 𝐵 ↔ ∀𝑦𝐴𝑥𝐵 𝑦𝑥)
5 ralcom 3092 . . 3 (∀𝑦𝐴𝑥𝐵 𝑦𝑥 ↔ ∀𝑥𝐵𝑦𝐴 𝑦𝑥)
6 dfss3 3578 . . . 4 (𝐴𝑥 ↔ ∀𝑦𝐴 𝑦𝑥)
76ralbii 2976 . . 3 (∀𝑥𝐵 𝐴𝑥 ↔ ∀𝑥𝐵𝑦𝐴 𝑦𝑥)
85, 7bitr4i 267 . 2 (∀𝑦𝐴𝑥𝐵 𝑦𝑥 ↔ ∀𝑥𝐵 𝐴𝑥)
91, 4, 83bitri 286 1 (𝐴 𝐵 ↔ ∀𝑥𝐵 𝐴𝑥)
 Colors of variables: wff setvar class Syntax hints:   ↔ wb 196   ∈ wcel 1987  ∀wral 2908   ⊆ wss 3560  ∩ cint 4447 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1719  ax-4 1734  ax-5 1836  ax-6 1885  ax-7 1932  ax-9 1996  ax-10 2016  ax-11 2031  ax-12 2044  ax-13 2245  ax-ext 2601 This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1483  df-ex 1702  df-nf 1707  df-sb 1878  df-clab 2608  df-cleq 2614  df-clel 2617  df-nfc 2750  df-ral 2913  df-v 3192  df-in 3567  df-ss 3574  df-int 4448 This theorem is referenced by:  ssintab  4466  ssintub  4467  iinpw  4590  trint  4738  oneqmini  5745  fint  6051  sorpssint  6912  iscard2  8762  coftr  9055  isf32lem2  9136  inttsk  9556  dfrtrcl2  13752  isacs1i  16258  mrelatglb  17124  fbfinnfr  21585  fclscmp  21774  noextenddif  31578  fneint  32038  topmeet  32054  igenval2  33536  ismrcd1  36780  dftrcl3  37532  dfrtrcl3  37545  sssalgen  39890  issalgend  39893
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