Theorem dfss3 3264

Description: Alternate definition of subclass relationship. (Contributed by NM, 14-Oct-1999.)

Assertion

Ref	Expression
dfss3	⊢ (A ⊆ B ↔ ∀x ∈ A x ∈ B)

Distinct variable groups:   x,A   x,B

Proof of Theorem dfss3

Step	Hyp	Ref	Expression
1		dfss2 3263	. 2 ⊢ (A ⊆ B ↔ ∀x(x ∈ A → x ∈ B))
2		df-ral 2620	. 2 ⊢ (∀x ∈ A x ∈ B ↔ ∀x(x ∈ A → x ∈ B))
3	1, 2	bitr4i 243	1 ⊢ (A ⊆ B ↔ ∀x ∈ A x ∈ B)

This proof depends on syntax axioms:   → wi 4   ↔ wb 176  ∀wal 1540   ∈ wcel 1710  ∀wral 2615   ⊆ wss 3258

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 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 proof depends on definitions:  df-bi 177  df-or 359  df-an 360  df-nan 1288  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-ral 2620  df-v 2862  df-nin 3212  df-compl 3213  df-in 3214  df-ss 3260

This theorem is used by:  ssrab  3345  eqsn  3868  dfpss4  3889  uni0b  3917  uni0c  3918  ssint  3943  ssiinf  4016  sspwuni  4052  rninxp  5061  fnres  5200  eqfnfv3  5395  funimass3  5405  dff3  5421  ffvresb  5432