Theorem dfss 3212

Description: Variant of subclass definition df-ss 3211. (Contributed by NM, 3-Sep-2004.)

Assertion

Ref	Expression
dfss	|- ( A C_ B <-> A = ( A i^i B ) )

Proof of Theorem dfss

Step	Hyp	Ref	Expression
1		df-ss 3211	. 2 |- ( A C_ B <-> ( A i^i B ) = A )
2		eqcom 2231	. 2 |- ( ( A i^i B ) = A <-> A = ( A i^i B ) )
3	1, 2	bitri 184	1 |- ( A C_ B <-> A = ( A i^i B ) )

Syntax hints:   <-> wb 105   = wceq 1395   i^i cin 3197   C_ wss 3198

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-5 1493  ax-gen 1495  ax-ext 2211

This theorem depends on definitions:  df-bi 117  df-cleq 2222  df-ss 3211

This theorem is referenced by:  ssalel  3213  onelini  4525  cnvcnv  5187  funimass1  5404  sbthlemi5  7151  dmaddpi  7535  dmmulpi  7536  tgioo  15268