Theorem difsnpss 3851

Description: (B \ {A}) is a proper subclass of B if and only if A is a member of B. (Contributed by David Moews, 1-May-2017.)

Assertion

Ref	Expression
difsnpss	|- (A e. B <-> (B \ {A}) C. B)

Proof of Theorem difsnpss

Step	Hyp	Ref	Expression
1		notnot 282	. 2 |- (A e. B <-> -. -. A e. B)
2		difss 3393	. . . 4 |- (B \ {A}) C_ B
3	2	biantrur 492	. . 3 |- ((B \ {A}) =/= B <-> ((B \ {A}) C_ B /\ (B \ {A}) =/= B))
4		difsnb 3850	. . . 4 |- (-. A e. B <-> (B \ {A}) = B)
5	4	necon3bbii 2547	. . 3 |- (-. -. A e. B <-> (B \ {A}) =/= B)
6		df-pss 3261	. . 3 |- ((B \ {A}) C. B <-> ((B \ {A}) C_ B /\ (B \ {A}) =/= B))
7	3, 5, 6	3bitr4i 268	. 2 |- (-. -. A e. B <-> (B \ {A}) C. B)
8	1, 7	bitri 240	1 |- (A e. B <-> (B \ {A}) C. B)

Syntax hints:  -. wn 3   <-> wb 176   /\ wa 358   e. wcel 1710   =/= wne 2516   \ cdif 3206   C_ wss 3257   C. wpss 3258  {csn 3737

This theorem was proved from 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 theorem 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 2478  df-ne 2518  df-v 2861  df-nin 3211  df-compl 3212  df-in 3213  df-dif 3215  df-ss 3259  df-pss 3261  df-sn 3741

This theorem is referenced by: (None)